Another idea that occurred to me was a lack of label for presumed trolls. We could show the author's current level next to their name in the by-line header. We would display no level for anonymous nor for sub-zero-XP authors.

I'd show the level name not the level number as I think the level number would be too easy to overinterprept as some indication of vetting. The level names would be a more playful addition. I think it would nicely enhance the XP game without over emphasis (which causes problems).

Did this (crudely; attribution needs a refactor which I may do later). We'll see what the reaction is.