In Ohio, repeat Dui offenders have a yelow, or orange colored license plate, that you can see from a mile away, that points out the fact that they have been convicted of a past Dui.
Wow...sort of like a scarlet letter. (Sorry, that's the first thing that came in my head...avid reader)
Perhaps not a bad idea...I would tend to drive very carefully and defensively if I saw an orange tag...