NC for this. I'm pissed off about this and am fantasising about revenge.
A house a few doors down from mine is being renovated, so there has been a builders van parked outside on the street. The other day I came home for lunch and parked for half an hour before heading back to the office. Our street is difficult to park on and the only space was directly behind their work van, so they way I was parked meant they couldn't open their back doors. That's the way it is on our street, it's very congested with parked cars so you park wherever you can find a space. Also I was parked outside my own bloody house.
Of course they still had access to the side door, but they must have got pissed off at the inconvenience because when I got to work I noticed the word 'spastic' written in large letters I. the dirt on the back of my work van. (Sorry, it is a truly horrible word and one I would never use, and any decent person would say the same) I'm 99% sure it was one of them because I saw them throw me a filthy look when I got out the van, and that word most definitely was not there when I parked as I checked the back to make sure I'd left a couple of feet clear behind me. I really can't imagine any of my neighbours doing that. Most were either at school/work and those who weren't are quiet and pleasant retirees.
If it had been a swear word or a rude drawing it wouldn't seem so bad. It's the fact they used such a vicious word that upset me. their van has no logos or company names on it so I've no idea who they are. I've checked their reg for tax and MOT and they're all up to date.
I should probably let it go, and there's probably not much I can do, but I have to admit I've been daydreaming about getting revenge on those little shits. Any ideas? 
nothing harmful or illegal of course.