Any guesses as to what this was for in 2nd edition UK Hobbits?

Signature mark?

Yes, that would be my guess.

- wellinghall

I haven't got a second edition, but the signature marks certainly appear (as you would expect) through the entire book on the 1946 (although the A is omitted). Presumably this is also the case on the second editions?

I will check, it looks like A* means that it is an earlier signature mark than A (though A by itself does not appear to exist, thanks Stu), I will check my copies to see if this is the case.

Thanks for all your help on this.