Burt said:
How about a simple laminated notice to the effect of "Insitu ropes and rigging are part of X club's dig, please do not remove"
I don't think that's a useful idea. It doesn't really solve anything because not everyone will do it (it may only be a small project not warranting such efforts) and so you'll end up with the same situation appearing. Also may it further encourage stealling as the thief can simple say, well there was no sign....?
This should really be protected by caving etiquette, not nanny state signs.
If people feel strongly enough about some "potentially" insitu ropes, and they cannot find out whose they are via the above mentioned means, then they could return and put a warning on them saying they are bad for whatever reason, and maybe even an upcoming date of removal (at least 2 months away), indicating clearly who's put the note up so contact can be made.
As an absolute minimum a note should be left in place after derigging to inform the owners of where to collect their gear from. Otherwise, stealling... I've had a small number of ropes taken from caves during active projects through the years, some from obscure locations, and not only does it leave a sour taste, but more importantly cancels your breakthrough trip you've been planning for weeks!