A good introduction to all things Crypto can be found here The one thread to link them all - https://bitcointalksearch.org/topic/overview-the-one-thread-to-link-them-all-1217042
You'll want to start with Signatures - how to create and verify them (not to mention PGP public keys for Satoshi, Admins, Staff as well as regular members. )
Basically, users are posting a BitCoin Wallet Address that they use (or is held in reserve) that they can at a later date sign a message from to say "Hey, my BCT Account was hacked, can you give it back please?"
The inherent danger is unless you BitCoin Wallet is password protected, someone can use your own PC/Lap top/portable device to sign a message and gain control of your BCT account. (think burglar or a person with (or without) a warrant to enter your premises).
This has also become the unofficial preferred way to present a signed message:
-----BEGIN BITCOIN SIGNED MESSAGE-----
-----BEGIN SIGNATURE-----
-----END BITCOIN SIGNED MESSAGE-----
Hope this helps.