Newbie: 50 characters.
Jr. Member: 150 characters.
Member - Hero: 4000 characters.
Is 4000 characters allowed for Member? When I was Member, I got error saying exceeded chracter length but it was less than 4000 characters.
One of the best threads for such questions is
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
True that it is the appropriate thread.
What you quoted doesn't answer his question. He asked "maximum character length" not "sig restrictions".
