I've got a cheapo car one that sticks to the inside of the screen...
... black & white photocopy goes in there and the original is in my wallet - the copy has got 'Theft Protection - Original With Owner' written across it.
Reasoning - a colour copy can look like it's trying to be 'legal' if you get my drift and you could get done for fraud or sommat. A black & white one is obvious and with the writing it's also obvious why it's there.
I've been asked to show the original a couple of times by both traffic wardens and police if they've been by the parked by when I gone back to it, but each time they've all said it's been a reasonable precaution.
Been doing this for about 19 years.
