If i'm right this is your Btc address
38SSicLEht2iUeaN73ADaNZftUgq8kqgET
On what i know is, all addresses that starts with 3 came from trading/exchange site. So, you can't really sign a message from it.
If you posted any address from your wallet, then you can sign that and give as a link on where you posted it.
Your basically selling your account, right??
yes your right I am using coins.ph wallet so it starts with 3 and yes I am only selling an account and that account didnt changr the password since the date if its creation.