I can sign a message with the address in my sig? As for collateral... Do you mean physical items??
edit:
Address: 1bongsiuorE3w1rAtLRphay7a1TSfJ4BB
Message: Signed message for polynesia
--bennybong from bitcointalk!
Signature: GxtxaU7g/waJCYEJ9qC/5ENLn93ZJWvtTyuLF7aoegvIB0VcRy2nCvBx7PoOxMOFdtCyyuQMZozsLPBcbjD/+Z8=
The point of asking for a signed message is to ensure that the account isn't hacked.
Have you posted this address on bitcointalk.org some time before (6 months ago or before that)?
If you haven't, then there is no point in the signed message.
Plus, it is always advisable to include today's date in the message (otherwise signed messages can be reused)