If they letters are stamped, that was done at the factory for some reason. Most engine rework people use an engraver signature of some kind, as far as I have seen. Randy signs "randy" with a number. Tom Lay was "T&L" with a number, Byron Barker signed "Byron" with a number , I think, Larry Foster signed L&J with a number, and that's all I can think of right now.
Type at you later,
Dan McEntee