Number plate is not so bad, you'll only get someone else's speeding and parking tickets... don't mind showing mine as its a cherished number, and too conspicuous to be cloned
VIN open up all sorts of other interesting possibilities if coupled with other info, and yes, I know that can be got off most cars these days easily by looking at the windscreen, but if I wanted to keep my prize VW Golf GTI ED30 or my XXXX for that matter, I would stay

Thom