Lets say you are selling 10 LTC @ 0.06 BTC and buyer agrees with you at that price and wants a signed message from you.
1-) You sign a message that includes the sale price and other terms and send it to potential buyer.
2-) Buyer keeps signed message for a possible conflict.
3-) If everything goes smoothly, deal is closed. However , either one of parties doesnot obey the deal , it will be easy to identify the who breaks the rules.
Possible conflicts:
Buyer sends 0.06 BTC and you can say that it isnt the sale price , it is 0.065 BTC.(But signed message says 0.06 BTC)
Buyer sends 0.06 BTC to an unknown BTC address that you arent specified in the signed message. So, you can prove that you didnt get the payment in case of wrong payment.
4-) Third party looks at the signed message and decides the wrong side of the deal. But please keep in mind a signed message doesnt prevent the scam. It just helps out the faulty part. If you are dealing transaction , use an ESCROW not to worry in future.
Oh, great !. Thanks Bittings so much ! I understood 95% about "sign a message" . Thanks again ! my great man !