diff --git a/assets/js/hooks/Mapper/components/mapInterface/components/SystemLinkSignatureDialog/SystemLinkSignatureDialog.tsx b/assets/js/hooks/Mapper/components/mapInterface/components/SystemLinkSignatureDialog/SystemLinkSignatureDialog.tsx
index 2d0031c6..aab55a43 100644
--- a/assets/js/hooks/Mapper/components/mapInterface/components/SystemLinkSignatureDialog/SystemLinkSignatureDialog.tsx
+++ b/assets/js/hooks/Mapper/components/mapInterface/components/SystemLinkSignatureDialog/SystemLinkSignatureDialog.tsx
@@ -138,10 +138,13 @@ export const SystemLinkSignatureDialog = ({ data, setVisible }: SystemLinkSignat
         let bookmarkIndex = info.bookmark_index;
 
         if (!bookmarkIndex) {
-          const calculated = calculateBookmarkIndex(systemSignatures, data.solar_system_source.toString(), signature.eve_id);
+          const sourceSystem = systems.find((s: any) => s.system_static_info?.solar_system_id === data.solar_system_source);
+          const systemUuid = sourceSystem?.id || data.solar_system_source.toString();
+          const calculated = calculateBookmarkIndex(systemSignatures, systemUuid, data.solar_system_source.toString(), signature.eve_id);
           bookmarkIndex = calculated.index;
           info.bookmark_index = calculated.index;
           info.bookmark_index_chained = calculated.chained;
+          info.bookmark_index_chained_letters = calculated.chainedLetters;
           updatedSignature = { ...signature, custom_info: JSON.stringify(info) };
         }
 
diff --git a/assets/js/hooks/Mapper/components/mapRootContent/components/MapSettings/constants.ts b/assets/js/hooks/Mapper/components/mapRootContent/components/MapSettings/constants.ts
index 152d180b..f177ab38 100644
--- a/assets/js/hooks/Mapper/components/mapRootContent/components/MapSettings/constants.ts
+++ b/assets/js/hooks/Mapper/components/mapRootContent/components/MapSettings/constants.ts
@@ -52,8 +52,8 @@ export const SIGNATURES_CHECKBOXES_PROPS: SettingsListItem[] = [
     prop: UserSettingsRemoteProps.bookmark_name_format,
     label: 'Bookmark Name Format',
     type: 'text',
-    placeholder: 'e.g. {i} {sig_letters} {dest_type} {size} {time_status} {mass_status}',
-    helperText: 'Variables: {i}, {I}, {sig_letters}, {sig}, {dest_type}, {type}, {size}, {mass}, {time_status}, {mass_status}, {temporary_name}, {description}',
+    placeholder: 'e.g. {chain_index_letters} {sig_letters} {dest_type} {size} {time_status} {mass_status}',
+    helperText: 'Variables: {index}, {chain_index}, {index_letter}, {chain_index_letters}, {sig_letters}, {sig}, {dest_type}, {type}, {size}, {mass}, {time_status}, {mass_status}, {temporary_name}, {description}',
   },
 ];
 
diff --git a/assets/js/hooks/Mapper/components/mapRootContent/components/SignatureSettings/SignatureSettings.tsx b/assets/js/hooks/Mapper/components/mapRootContent/components/SignatureSettings/SignatureSettings.tsx
index 88b59614..cd9aa5d2 100644
--- a/assets/js/hooks/Mapper/components/mapRootContent/components/SignatureSettings/SignatureSettings.tsx
+++ b/assets/js/hooks/Mapper/components/mapRootContent/components/SignatureSettings/SignatureSettings.tsx
@@ -131,10 +131,13 @@ export const SignatureSettings = ({ systemId, show, onHide, signatureData }: Map
 
           let bookmarkIndex = info.bookmark_index;
           if (!bookmarkIndex) {
-            const calculated = calculateBookmarkIndex(systemSignatures, systemId, out.eve_id);
+            const currentSystem = systems.find((s: any) => s.id === systemId);
+            const solarSystemIdStr = currentSystem?.system_static_info?.solar_system_id?.toString() || systemId;
+            const calculated = calculateBookmarkIndex(systemSignatures, systemId, solarSystemIdStr, out.eve_id);
             bookmarkIndex = calculated.index;
             info.bookmark_index = calculated.index;
             info.bookmark_index_chained = calculated.chained;
+            info.bookmark_index_chained_letters = calculated.chainedLetters;
             out.custom_info = JSON.stringify(info);
           }
 
diff --git a/assets/js/hooks/Mapper/helpers/bookmarkFormatHelper.ts b/assets/js/hooks/Mapper/helpers/bookmarkFormatHelper.ts
index b7d7d2a6..668393e3 100644
--- a/assets/js/hooks/Mapper/helpers/bookmarkFormatHelper.ts
+++ b/assets/js/hooks/Mapper/helpers/bookmarkFormatHelper.ts
@@ -69,17 +69,29 @@ const formatDestString = (dest: string | null | undefined): string => {
   return dest.charAt(0).toUpperCase() + dest.slice(1);
 };
 
+const numberToLetters = (num: number): string => {
+  let letters = '';
+  while (num > 0) {
+    const mod = (num - 1) % 26;
+    letters = String.fromCharCode(65 + mod) + letters;
+    num = Math.floor((num - mod) / 26);
+  }
+  return letters;
+};
+
 export const calculateBookmarkIndex = (
   systemSignatures: Record<string, SystemSignature[]>,
-  currentSystemId: string,
+  currentSystemUuid: string,
+  currentSolarSystemId: string,
   currentEveId: string,
-): { index: number; chained: string } => {
+): { index: number; chained: string; chainedLetters: string } => {
   let parentBookmarkIndex: string | undefined;
+  let parentBookmarkIndexLetters: string | undefined;
 
   for (const [sysId, sigs] of Object.entries(systemSignatures)) {
-    if (sysId === currentSystemId.toString()) continue;
+    if (sysId === currentSystemUuid || sysId === currentSolarSystemId) continue;
 
-    const parentSigs = sigs.filter(sig => sig.linked_system?.solar_system_id?.toString() === currentSystemId.toString());
+    const parentSigs = sigs.filter(sig => sig.linked_system?.solar_system_id?.toString() === currentSolarSystemId);
     for (const parentSig of parentSigs) {
       const parentInfo = parseSignatureCustomInfo(parentSig.custom_info);
       if (parentInfo.bookmark_index_chained != null) {
@@ -91,12 +103,24 @@ export const calculateBookmarkIndex = (
           parentBookmarkIndex = String(parentInfo.bookmark_index);
         }
       }
+
+      if (parentInfo.bookmark_index_chained_letters != null) {
+        if (!parentBookmarkIndexLetters || String(parentInfo.bookmark_index_chained_letters).length < parentBookmarkIndexLetters.length) {
+          parentBookmarkIndexLetters = String(parentInfo.bookmark_index_chained_letters);
+        }
+      }
     }
   }
 
-  const currentSigs = systemSignatures[currentSystemId.toString()] || [];
+  const currentSigsRaw = [
+    ...(systemSignatures[currentSystemUuid] || []),
+    ...(systemSignatures[currentSolarSystemId] || [])
+  ];
 
-  const existingIndices = currentSigs
+  // Deduplicate in case both keys map to the same or overlapping arrays
+  const uniqueCurrentSigs = Array.from(new Map(currentSigsRaw.map(sig => [sig.eve_id, sig])).values());
+
+  const existingIndices = uniqueCurrentSigs
     .filter(sig => sig.eve_id !== currentEveId)
     .map(sig => parseSignatureCustomInfo(sig.custom_info).bookmark_index)
     .filter((i): i is number => typeof i === 'number' && i > 0);
@@ -107,8 +131,9 @@ export const calculateBookmarkIndex = (
   }
 
   const chained = parentBookmarkIndex !== undefined ? `${parentBookmarkIndex}${i}` : `${i}`;
+  const chainedLetters = parentBookmarkIndexLetters !== undefined ? `${parentBookmarkIndexLetters}${i}` : numberToLetters(i);
 
-  return { index: i, chained };
+  return { index: i, chained, chainedLetters };
 };
 
 export const formatBookmarkName = (
@@ -121,11 +146,17 @@ export const formatBookmarkName = (
   let result = formatStr;
   const info = parseSignatureCustomInfo(signature.custom_info);
 
-  // Replace {i}
-  result = result.replace(/\{i\}/g, () => bookmarkIndex.toString());
+  // Replace {index}
+  result = result.replace(/\{index\}/g, () => bookmarkIndex.toString());
 
-  // Replace {I}
-  result = result.replace(/\{I\}/g, () => info.bookmark_index_chained || bookmarkIndex.toString());
+  // Replace {chain_index}
+  result = result.replace(/\{chain_index\}/g, () => info.bookmark_index_chained || bookmarkIndex.toString());
+
+  // Replace {index_letter}
+  result = result.replace(/\{index_letter\}/g, () => numberToLetters(bookmarkIndex));
+
+  // Replace {chain_index_letters}
+  result = result.replace(/\{chain_index_letters\}/g, () => info.bookmark_index_chained_letters || info.bookmark_index_chained || bookmarkIndex.toString());
 
   // Replace {sig_letters} (first 3 chars of eve_id)
   const sigLetters = signature.eve_id.substring(0, 3).toUpperCase();
diff --git a/assets/js/hooks/Mapper/types/signatures.ts b/assets/js/hooks/Mapper/types/signatures.ts
index ac4cf96c..eb68d693 100644
--- a/assets/js/hooks/Mapper/types/signatures.ts
+++ b/assets/js/hooks/Mapper/types/signatures.ts
@@ -35,6 +35,7 @@ export type SignatureCustomInfo = {
   mass_status?: number;
   bookmark_index?: number;
   bookmark_index_chained?: string;
+  bookmark_index_chained_letters?: string;
 };
 
 export type SystemSignature = {