Incorporate the character's name into the item used to represent the skillcape (or other thing) in some way, in a manner that can be erased and replaced with another name by GMs to save on cost. Wet-erase markers are probably the way to go here: they're cheap and players can't cheat them without some effort. If someone does cheat the system even though you are using said markers, you should probably consider not playing with them rather than increasing security measures. If you run your LARP with an entrance fee, at large conventions, or in some other manner which means kicking bad players is less possible, incorporate both character names and a GM autograph into the item and the same color consistently for all of a single player's stuff, while using a wide variety of colors in general.
If possible, especially if you aren't running a game with a massive number of players, take the time to learn your players' characters by reviewing their sheets between sessions. Encourage your co-GMs to do so as well. Knowing in general who can do what how well is the best defense against shenanigans, and keeps honest player mistakes (2+2=22, I was cold so I borrowed his jacket (which happens to have a sticker marking it as +5 full plate), etc) dealt with quickly and simply. Besides, you can't really be a good GM if you don't know the PCs. This will also discourage cheating via items because it reminds people that the item is just a symbol that represents the number on the character sheet for the purpose of convenience. Cheaters will realize they need to get to the sheets if they really want to mess with the game.
Make sure you have as much overlap between the player and GM communities as possible. Characters don't exist in a vacuum and the in-character friends, rivals, enemies, children, etc. of a cheater will notice when his stats suddenly go whack even if you don't. If some of these people are also your out-of-character friends they'll let you know somethings up and you'll find the inevitable "they just have it out for me" defense a lot easier to deal with.
Source: Helped out at a BAM thing a couple of times, where they seemed to make use of the last two bullet points. Helped out at a boffer-larp thing where the GMs made use of point 1 in the more extreme version, as well as point two and literally kept case files on their players and their history of cheating, poor sportsmanship, and general jerkishness. Most of the files were basically empty, but a couple of them were very, very full. Some people are jerks.