Help identify a book containing SIGNET

I have a scrap of paper upon which I wrote some cryptic notes about a book I was reading. Unfortunately, I failed to record anything that would help me identify the book. The notation most likely to be unique is a reference to SIGNET, written in all caps (and I never write in all caps, so it must have appeared that way in the book). There are also references to robots and martial arts, but the information on the scrap is too scant for me to say whether these were important to the plot or passing mentions. SIGNET seems the best clue. (I realize it's still a very long shot that this is enough for anyone to make an ID.)

The paper scrap dates from the mid 1990s; I have no idea when the book might have been published. It is almost certainly on my shelves somewhere among the couple thousand volumes I own, because I never get rid of anything, but I hope this forum will lead to a quicker answer than paging through all of them!