Is someone spray painting my cats?

[McMom]

I have 3 cats, and they spend their days outside.
We have lots of neighbours, and I imagine that they tend to sneak into their gardens (as do their cats ours).

A few days ago, 1 of my cats came home with green stuff on his back, I didn't think much of it, I thought he'd gotten into some rubbish somewhere.

Then this morning, one of my other cats came home with green all over his face, it looked like spray paint, really bright green.

I'm thinking maybe someone sprayed them to shoo them away, which i'm not ok with -- but More to the point --- could this do any damage if it got into their eyes, or mouth....?
--- keeping them indoors is not an option, they like their freedom, and the back yard isn't big enough.

And as for a police report -- I don't think I would have any grounds, I mean, its their proporty -- My cats are basically trespassing...
rmbrruff -- "Unless the issue is that you don't want to clean a litter pan" --- Ugh, No, the issue is that I want my cats to have a good quality life, and have freedom to explore outside and not be cooped up inside all day like most poor cats. (and don't bother saying "this is the price you pay, your cats will die from being outside", because no, I will make sure something is done) -- Don't want to clean the litter pan indeed.... Cats are outdoor creatures.