Royal Letters are part of the collectibles in Assassin’s Creed Syndicate. Once you collect all the Royal Letters, you’ll unlock “A Life in Letters” trophy / achievement. Here we have all the Vintage Beer Bottle Locations in Assassin’s Creed Syndicate.
The Royal Letters collectibles are very rare, so they are no way any merchant to sell treasure maps with the location for this collectible. The Good news is that these collectible are fairly close together in Buckingham, Westminster so use eagle vision when near this location and it will automatically show up on your map.
Make sure you have a High Skilled Eagle Vision which will make it easy to hunt all the collectibles in the game. Once you start picking up the Royal Letters, they will be saved and you can keep a track on it on the map. So without any further Ado here is the locations for all the Royal Letters in Assassin’s Creed Syndicate.
All the Royal Letters are Spread in Westminster near the Buckingham Palace, except for one which I have marked in red is inside the Palace. So use you eagle Vision near that area and you’ll easily locate the Letter. Once you obtain all the Royal letters you’ll be awarded “A Life in Letters” trophy / achievement.