I use blockchain.
I even tried to create a new blockchain and test it there, I made a signature, used brainwallet to verify it and it was not able to verify.
I made sure there were no extra symbols or spaces but it still says invalid :/
blockchain is the vessel behind for example bitcoin.
you are probably talking about blockchain.info the website?
ofcourse he is talking about blockchain.info/wallet, I am sure he's not asking how to sign a message with bitcoin blockchain.
OP can you post a signed message here, Just make sure to
add the today's date to it and a line for "testing purpose only", and we'll see if it verifies or not.