No matter how well your gear is marked, if there's a thief on the boat with you, your stuff is subject to getting ripped off. But, after reading that great story about the camera showing up in Key West
(what a great story), I'm rethinking how to mark my gear.
It's obvious that the tags, colored vinyl tape, sharpies and paint sticks work great. Since I test a lot of gear, I get to return it 'in it's original form' and don't get to make permanent markings. However, for my personal gear, everything is modified in some way making it unique. On wetsuit booties, mine have a 'button hole' sewn in the tops so I can hook a carabiner in them to hang them up. If a button hole won't work, I've installed a brass grommet (but location is important) to facilitate drying. Inside my flashlights there's a rolled up address label. My camera gear now has my full address inside the housing/strobe.
If you're diving at a resort where they have lockers to store your gear overnight, it's a great idea to make sure your smaller items are all in a distinctive mesh bag. This not only keeps the gear together, you'll see quickly if someone else has a similar bag.
From experience, it seems that those divers who develop a 'systematic method' for dealing with their gear will not have a problem. Those divers who have things scattered about or have to make six trips to their car when loading the boat might be the ones who need some help. I've been on boats where divers leave their cameras under a towel and totally forget it till the next day. I could see forgetting a weight pouch, but not a camera... don't forget to look in the rinse bin before leaving the boat. Most all dive operators will help you remember, but really it's your job as a diver to keep track of your gear and have it well marked so not to be confused with other divers.
Happy Diving !!!