Or, what about different/new badges for milestones?
I like your idea, and it would work having 3 "Constable/Sheriff" badges after being here 3 years, but another idea would be to have something like:
- Year 1 (only) - Constable/Sheriff badges
- Year 3 (only) - New badges (need naming/thinking up)
- Year 5 (only) - New badges (need naming/thinking up, different to year
Then rather than recognition for being a mod for 3 years is you have "3" Constable/Sheriff badges and someone else only has "2", you actually have an entirely different badge only earned for being a mod for 3 years.
EDIT in response to comments
If we only award the same badge each year, someone who's been a moderator for 8 years has the same badge type as a moderator only in their 2nd year. Not much to showcase really is it?
Sure, their "count" is different (total 8 badges VS 2 badges) but it's devalued having the same badge type.
Alternatively, having a badge type which can only be earned after being here X years stands out more as a medal of honour.
At glance, users can see "ooh, they've got the mega-mod badge"..
(yeah, "mega-mod" badge, is just for sake of an example..)