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
Then newbies will be less effective advertisers, which would hopefully significantly reduce the incentive for low-content posts. And when people become capable of effectively advertising through their signatures, they'll have invested a lot of time into their accounts, and they won't risk being banned by spamming.
You are a Full Member and that's enough to put some colorful ads with links in the signature area. Your trust score doesn't make you ineligible, accounts that have neutral and negative trust can also get ads in their signature. It depends on the campaign manager, they all have different criteria. The more quality posts you make, the better your chances of being selected.