DIY Road marking

That ought to be fine. Unless you live in Salisbury.

Stick a hi-vis vest on and you can do whatever you like all day long.

Don't work too fast either, that's a dead giveaway.

libertyne correct, hi-vis and clipboard should suffice. Might even get a cuppa n' bacon sandwich from a similarly outraged neighbour.

During the Blitz some thieves would turn up at a bombed-out house, put an ARP warden's helmet on and then ask passersby to help them load up their vehicle with stuff they were looting from the house.  People would help because of the helmet.

They wouldn't need to wear a helmet to fool people these days. They couldn't care less anyway.
If you call the police they're more likely to arrest you for having the cheek to call them out.