This is getting more and more common.
Ive been to a few big (like over 1000 ppl) LAN tournaments with people walking around with their monitors and comps in their arms. Theft is kept to a minimum (although it will always go on) by two ways:
1. A sort of neighbourhood watch system, ie teams could keep and eye out for each other, although easier said than done
2. An I.D and badge system, a tag around the players neck and a sticker on the marker with both name and an ID number. This could be checked by a few people walking around to make sure they match obv.
Just some ideas, wont help for other equipment lost/stolen, and whether players will want to walk around with tags and stickers all over them and their "babies" is another matter.
Hope you guys find your stuff tho