Reddit mentions of Pro Tape 15410 Gaffers Tape, 50 yards Length x 2" Width, Orange

Yep! https://www.amazon.com/Pro-15410-Gaffers-Length-Orange/dp/B000SZ3RZ2

I wouldn't bother with biners, but for more expensive stuff a little strip of orange gaffer tape works well, and has a bunch of advantages:

1. It's removable and won't leave any sticky residue...but thieves probably won't know that (it looks just like regular cloth tape) so they may not try to remove it
   
2. Despite #1 it's very sticky and I've never had any come off unless I wanted it to, long as you tape it onto a clean and reasonably smooth surface.
   
3. If you pick a bright color it's easily visible from a distance (unlike engraving or that kind of thing)
   
4. You can write on the tape (for example, name and address to return lost gear)
   
5. If you really want to get funky you can create designs/patterns to make your stuff even more easily identifiable
   
   I started doing this with my camera gear because when I'd be doing freelance shoots as part of a team, other people would have the same bodies and/or lenses and when you're switching lenses around and stuff it's easy to lose track of whose is whose if they're not marked. But then I realized it would work well for basically anything, and now I use it for everything.
   
   For example, I really like it for luggage at the airport. Basically everyone has similar looking gray or black luggage, so it'd be easy for someone to grab yours at the carousel and walk away (intentionally or by accident) before you even notice. But put some big-ass orange Xs on that same luggage with tape and it stands out and becomes easy to spot.