When I certified in May 2000, my instructur told the class that more and more boat captains and dive shops are asking to see logs when you wont to do anything beyond 60 ft.
When I did my first post cert. dives, I hired a DM to come with my husband and I (in Key West), the first couple of dives, and she offered (and did) sign my log book when she saw that I was keeping one. During dives I have taken after that, the shop offered to stamp my log with their name and address. This works great for me, in case I ever want to go back and dive with them, as I now have name, address and telephone number.
My practice since my initail, positive, experience is to try and find someone "in charge" (i.e. DM) or whomever is along to sign my log. My husband does this too, as it is in keeping with the practice required by the FAA he has for his piloting logs. -Starfish