Quote for reference please. Thank you!

12B5m4bsgKjz5j5j9fBFYzXDDxua2zgMLW

-----BEGIN BITCOIN SIGNED MESSAGE-----
This is scumbag from bitcointalk.org and today is 2015.09.22
-----BEGIN BITCOIN SIGNATURE-----
Version: Bitcoin-qt (1.0)
Address: 12B5m4bsgKjz5j5j9fBFYzXDDxua2zgMLW

IOfFlSgkIN4Hr3LUWjRSp3YjLmTEY11AUK+rubn7iruhWn3vqH95VXYnINiN1qLa5xwK6DghAXop9yef1PTK/L0=
-----END BITCOIN SIGNATURE-----

Yes. Quoted. . Verified on BlockTrail.

It is always better to sign a message when you post your address.
Anyway this is good too if you know how to sign a message.
As i know "3" prefix is for xapo and bit-x if i am not wrong and in xapo you can not sign a message..

Then it is not good, because a signed message can prove the ownership of your bitcoin address.

If you use any other bitcoin wallet then try to sign a message and include this address too.