There are restrictions on the various ranks wrt signatures. From here (
https://bitcointalk.org/index.php?topic=178608.0).
- Newbie: No styling (including links) allowed. Max 50 characters.
- Jr. Member: Links allowed. Max 150 characters.
- Member: Unlimited length.
- Full: Color allowed.
- Sr. Member: Size allowed
- Hero: Background color allowed