How to prevent theft- A suggestion.

[misaxamane]

1. NEVER set your things down and look away. Very bad.
2. Don't set something down and WALK away. It's common sense.
3. If you have a friend with you, and you have to pose for a picture, GIVE YOUR FRIEND YOUR STUFF.
4. Unless your friend has to be in the photo with you, put you bag/backpack/purse/wallet on the floor in front of you.
5. Don't put anything down in highly-crowded areas. 0.0

[nekovamp13]

If you have a bag or something, try to make it a prop! You wouldn't have to put it down for pictures!!!
Cosplaying as Sven, I would have a "suitcase" that is a prop, and so can take pictures with it in my hand!

[xxxchihiroxxx]

xD my trick, fit pockets in your cosplay where you wouldnt expect there to be any.

that and after buyihg stuff if you got a room at the con hotel go deposit it there

[misaxamane]

Or if you can't have pockets, like you have a dress, wear a little button-over pouch. Easy to sew on!

[princessfrodo]

If you do have a prop, label it.  Especially if it's a prop from a popular cosplay.  I know I put Spider-Man stickers on the inside of anything and everything that they will stick to when I go to a LAN, and that's nearly the same thing.  Minus costumes.  And walking.  Or moving.

I hate to say it, but never trust anyone.  There are tons of great people that go to Cons, but never hand your bag to a stranger and then turn your back.  They can easily walk away with your stuff.

[princessmoon]

Don't leave your stuff on your seat to go to the bathroom during a show/panel/contest. A few people did that next to me @ the con, and you people are lucky I notice my surroundings and remember what you look like. Other people came to claim their stuff and THIS nice person POLITELY asked to wait for the owner of said items. *sigh* Turns out...the lucky duckies didn't know those people... 

Don't be a target for potential theft!!

One year I didn't have any pockets and didn't want to carry tons of stuff. I brought my camera in a wrist case and put money+1 credit card+drivers license into my knee length socks. That was a last resort and worked well!

[jaybug]

Put your name on your stuff.
Be alert to your surroundings.

[kylite]

if nothing else, seek out a yojimbo. We are often stationed and can watch over things (TEMPORARILY)

[nekovamp13]

Bring friends!!!! They're your best bet for keepin' stuff safe! Especially if you have a friend who isn't in cosplay willing to do so!

[misaxamane]

Unless your friends are in your cosplay group!

[nekovamp13]

Then you just go with what others said...