A little Unity utility to check for shortcut key collisions because it's hard to know if you're duplicating one from anywhere else.

ShortcutCollisionChecker.cs

using UnityEngine;
using UnityEditor;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text.RegularExpressions;

// Little utility to check for shortcut key collisions because it's hard to 
//  know if you're duplicating one from anywhere else.
//
// Put this inside a /Editor/ Folder
//
// ## Contact
// Any questions or bug reports - email me!
// Chris McLaughlin - chris@vitei.com
//
public class ShortcutCollisionChecker{

    [MenuItem("Custom/Vitei/Code/Check For Shortcut Collisions #%C")]
    static void CheckForShortcutCollisions() {
        
        Dictionary<string, string> shortcuts = new Dictionary<string, string>() { //populate with unity default keys, probably missing some
            {"_Q", "[Unity Built In] Pan"},
            {"_W", "[Unity Built In] Move"},
            {"_E", "[Unity Built In] Rotate"},
            {"_R", "[Unity Built In] Scale"},
            {"_T", "[Unity Built In] Rect Tool"},
            {"_Z", "[Unity Built In] Pivot Mode toggle"},
            {"_X", "[Unity Built In] Pivot Rotation Toggle"},
            {"_V", "[Unity Built In] Vertex Snap"},

            {"#%N", "[Unity Built In] New empty game object"},
            {"#&N", "[Unity Built In] New empty child to selected game object"},
            {"%&F", "[Unity Built In] Move to view"},
            {"#%F", "[Unity Built In] Align with view"},
            {"#F", "[Unity Built In] or double-F Locks the scene view camera to the selected GameObject"},

            {"%1", "[Unity Built In] Scene"},
            {"%2", "[Unity Built In] Game"},
            {"%3", "[Unity Built In] Inspector"},
            {"%4", "[Unity Built In] Hierarchy"},
            {"%5", "[Unity Built In] Project"},
            {"%6", "[Unity Built In] Animation"},
            {"%7", "[Unity Built In] Profiler"},
            {"%9", "[Unity Built In] Asset store"},
            {"%0", "[Unity Built In] Version Control"},
            {"#%C", "[Unity Built In] Console"},

            {"%Z", "[Unity Built In] Undo"},
            {"%Y", "[Unity Built In] (Windows only) Redo"},
            {"#%Z", "[Unity Built In] (Mac only) Redo"},
            {"%X", "[Unity Built In] Cut"},
            {"%C", "[Unity Built In] Copy"},
            {"%V", "[Unity Built In] Paste"},
            {"%D", "[Unity Built In] Duplicate"},
            {"#Del", "[Unity Built In] Delete"},
            {"_F", "[Unity Built In] Frame (centre) selection"},
            {"%F", "[Unity Built In] Find"},
            {"%A", "[Unity Built In] Select All"},
            {"%P", "[Unity Built In] Play"},
            {"#%P", "[Unity Built In] Pause"},
            {"%&P", "[Unity Built In] Step"},

            {"#%1", "[Unity Built In] Load Selection 1"},
            {"#%2", "[Unity Built In] Load Selection 2"},
            {"#%3", "[Unity Built In] Load Selection 3"},
            {"#%4", "[Unity Built In] Load Selection 4"},
            {"#%5", "[Unity Built In] Load Selection 5"},
            {"#%6", "[Unity Built In] Load Selection 6"},
            {"#%7", "[Unity Built In] Load Selection 7"},
            {"#%8", "[Unity Built In] Load Selection 8"},
            {"#%9", "[Unity Built In] Load Selection 9"},
            {"%&1", "[Unity Built In] Save Selection 1"},
            {"%&2", "[Unity Built In] Save Selection 2"},
            {"%&3", "[Unity Built In] Save Selection 3"},
            {"%&4", "[Unity Built In] Save Selection 4"},
            {"%&5", "[Unity Built In] Save Selection 5"},
            {"%&6", "[Unity Built In] Save Selection 6"},
            {"%&7", "[Unity Built In] Save Selection 7"},
            {"%&8", "[Unity Built In] Save Selection 8"},
            {"%&9", "[Unity Built In] Save Selection 9"},

            {"%R", "[Unity Built In] Refresh"},

            {"#&A", "[Unity Built In] Toggle Gameobject Active"},

            {"%#C", "[Unity Built In] Open Console"},
        };
        
        // Get all our c# files
        string[] assetPaths = AssetDatabase.GetAllAssetPaths();
        List<string> allCsFiles = new List<string>();
        foreach (string assetPath in assetPaths) {
            if (assetPath.Contains(".cs")) {
                allCsFiles.Add(assetPath);
            }
        }

        // Tell the user we're about to do some serious work that might take time.
        EditorUtility.DisplayProgressBar("Checking for Shortcut Collisions", "", 0);

        // Run through every line in every file looking for "[menuitem]"s with shortcuts, and make a list of them
        int shortcutCount = 0;
        int collisionCount = 0;
        Regex regex = new Regex("\\[MenuItem.*\\(\"(.*) ([&#%_]*[a-z])\".*]");
        for (int i = 0; i < allCsFiles.Count; i++) {

            // update the progress bar every 10 files.
            if (i % 10 == 0) {
                EditorUtility.DisplayProgressBar("Checking for Shortcut Collisions", i + "/" + allCsFiles.Count, (float)i / (float)allCsFiles.Count);
            }


            StreamReader sr = new StreamReader(allCsFiles[i]);
            string line;
            while ((line = sr.ReadLine()) != null) {
                Match m = regex.Match(line);
                if (m.Success) {
                    shortcutCount++;
                    string sortedKeys = new string(m.Groups[2].ToString().OrderBy(c => c).ToArray());

                    // if this shortcut already exits, print it out to the console
                    if (shortcuts.ContainsKey(sortedKeys)) {
                        string sks = sortedKeys.ToUpper().Replace("#", "Shift ").Replace("%", "Ctrl ").Replace("&", "Alt ").Replace("_", " ");
                        Debug.Log("Collision: " + sks + " - <b>\"" + m.Groups[1] + "\"</b> vs <b>\"" + shortcuts[sortedKeys] + "\"</b>", AssetDatabase.LoadAssetAtPath(allCsFiles[i], typeof(object)));
                        collisionCount++;
                    }
                    else {
                        shortcuts.Add(sortedKeys, m.Groups[1].ToString());
                    }
                }
            }
            sr.Close();

        }

        EditorUtility.ClearProgressBar();

        // Print out overview of how well (bad?) we did
        Debug.Log("" + collisionCount + " collisions in " + shortcutCount + " shortcuts in " + allCsFiles.Count + " cs files");
    }
}