In short you need to be higher rank to add signatures read the link above for more information.
In shorter, Newbies are allowed signatures up to 50 characters from day 1.
Perhaps the allowed signature styling should change with activity score / membergroup. Like:
- Newbie: No styling (including links) allowed. Max 40 characters.
- Jr. Member: Links allowed. Max 100 characters.
- Member: Unlimited length.
- Full: Color allowed.
- Sr. Member: Size allowed
- Hero: Background color allowed
mod edit: Removed quotes of posts that have been removed.