I've noticed a lot of defaced license plates lately. Not weathering and fading (as in the last Wisconsin plate design fiasco), but scraped and dented. O(1%) of the cars I see are hard to read the plates on.
Maybe this is a new vandalism fad. That would be the best possibility.
UPDATE. O(1%) means of the order of 1%. Give or take a little.
The pilot in our Wednesday Bible study suggested that the defacement might be to foil the toll cameras.