I think tinyfaery is on to something. Sometimes, there are city ordinances that stipulate how many vehicles can be parked at a house, or that any vehicle that is parked on the street has to be in running order….. If the van doesn’t go, you might be able to get a tow order for it. Depending on where you live, you can call your town or county clerk, or city manager. Each city has a lawyer that acts on it’s behalf and should know what the rules are.
Is there somewhere else the neighbours could park the thing? Push it into their back yard where no one can see it? Have you tried talking to them telling them it looks like hell and you think it would be good for the neighbourhood if they could move it somewhere less of an eyesore?
I had neighbours with a bright light shining into our house… we couldn’t work out what the heck they were doing. It went on for weeks. We finally got their phone number and called them… They had no idea it was bugging us, said sorry and turned it off. Sometimes, people can be nice.