Supposedly it's "larger" than a regular members signature is allowed to be. I got messaged about mine as well, but I also had a bunch of text underneath. They say we're only allowed 5 lines as 'non-contributing' members of the site. And by contributing, they don't mean participating in active discussion but throwing money at them. Back to the point, the signature is closer to 7 lines (I measured with my eyes) but I don't really see how that's enough of an overage to necessitate being removed, but the overlords here can be a bit irrational with some of their authority stick waving.
TLDR; Put it back in your signature.