The license plates do nothing for radar waves unless the plate is heading straight for the radar gun like trying to see yourself in a mirror. Lasers work on plates because the plates are designed to retro-reflect visible light (but not radar).
Radar is retro-reflected beautifully by perpendicular junctions like the welded joints found throughout the tridon safety cell. Anecdotally, there's a reflective wall in a local shopping mall that's a bit creepy because as you walk toward it, all you see is multiple copies of yourself. Go right, go left, it doesn't matter: you see only yourself (or the sliver of view you're in). These are a series of 2-surface corner reflectors, one for each image you see. A 3-surface corner reflector will leave you always seeing your eye in the middle where the 3 surfaces come to a point: the corner of a cube. It's these 3-surface corner reflectors that make cars such easy radar targets.
Engineering can be great fun!
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