And yes I'm still new to this signed message thing, and i got a question, does signing a message with said address need the private key?
Of course, you need your private key to access your old wallet and sign messages. But if you've never posted that address or PM sent that address to someone in the past, I think maybe your request will be rejected. So the bottom line is that any bitcoin address you have used in the past on forum will serve to prove you are the real owner.