I use a couple of color permanent pen, not really 'Sharpie' but similar with big tip, and painted on my fin front and back. My fin is all-black from the factory, so painted it help distinguished from others' onboard the boat. and it does help a bit underwater. I use White, Neon Green, and Bright Blue. I just traced the logos and stamped-out part of the fin. I'd have to re-paint it once a year, though.
Also, another trends in SE Asia (I'd seen them in Thailand, Malaysia, Indonesia)is use a colorful quick-dry fabric hat with chin strap, instead of a hood. Something similar to what in this
Link. It also help protect you from the sun while on surface. Also, ornated hood like what in this
Link would also help identify you/your buddy underwater. (Well, most of the design fit the ladies rather than the guys.)
You can also use the 'Buff' type of fabric headwear on your head, but this doesn't help with exposure protection.
Some ppl also use a small float toy tied to their first stage... but that kind of increase risk of entanglement if you're concerned on it.