Looks like one of the facsimile signatures. George Allen and Unwin published a few of these facsimile signature editions - although I’m not sure I’ve ever seen one in Smith.
It looks to me like someone has tried to make a 'stamp' of Tolkien's signature which they have then applied to the book.
Faramond wrote:
The Samarillion? I haven't read it before. Is it an account of the Elder Days written by a Gamgee?
I found a picture of the author...