Should I put a mark in the trust, or is it the work of moderators?
It's a job for the mods. Pick a post made by the ban evader (preferably one that proves they are evading their ban) and report it. Be sure to state in your report that the report is for ban evasion (along with the identity of the originally banned account and a link to evidence, if it's not obvious from the post) and the mods will deal with it.
Or is it simply not paying attention?
Mods aren't gods; they don't see all. That's why you're encouraged to report rule violations whenever you see them.
