This doesn't help you now, but in studios I've worked in, there is a mic inventory sheet kept inside the mic locker. Prior to session start and again as the clients are tearing down I do a mic inventory. Mics have never been lost/stolen during one of my sessions.
Mics have been stolen on other occasions when this simple task was not done. I heard of one session where someone got in from outside and ran off with a '57 while a session was in progress!
On the cable side, I've had people leave cables and I've had no idea where they came from.