Meter Maids have been able to do this for years. I got a ticket by one at least 5yrs or so ago for not having one displayed on my trailblazer. The funny thing was, there was a cop in a cruiser right beside my car when I got back to it. I inquired about it with him, and he looked at my rear plate, saw current registration, saw front plate displayed in windshield, and said he wasn't sure why the MM ticketed me. He saw no issue with my vehicle, and he went on his way. Ha ha. Ohh well. Lesson learned.