As mentioned above, you should use bbcode to create a signature.
Use ASCII character " █ " to draw logos as you can't insert images in the signature space.
keep in mind that there are restriction on signatures according to member's ranks:
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
You can use an image as avatar if you are full member or higher and it should not be animated.