I guess I'm the exception, as every one of my almost 1000 dives has a buddy or DM or other signature. ABout 200 of them have Debbie's signature. I get them for the same reason an autograph collector gets autographs. I like to follow up with dive buddies I've met and dived with. So they sign and write their contact info into my book. I carry my last 50 or so dive logs plus blank pages on all trips. On a liveaboard trip, or training weekend, signatures are a snap. If I am on a trip with a friend, they often will sign at the dive day. I have become the designated "dive logger" when I travel, and others often copy data out of my book. It's all fun to me, and when I cannot dive, I like to use the log book to review and remember trips.
DivemasterDennis