In reply to rockwing:
Just be careful about marking any load-bearing textiles. I think UIAA recommend against marking things like slings and ropes with marker pen or tape as the solvents involved can weaken them. Harnesses usually have a nice white care label that you'd be able to just write a number on with a fine-tip marker pen. A lot of thicker nylon slings which have professional PPE crossover usually have nice big white labels on them for identification purposes too (that you could write on).
If it's mostly clothing and harnesses, would a plain old valve tag on a keyring work?
