I'd suggest something involving lasers except you said no vandalism so that's out. I don't think the EFF would be able to help directly but you could reach out to info@eff.org and see if they can put you in touch with an attorney who might be able to do more. A search for "[your location] bar association" is another possibility. Most places I've been will have somebody willing to talk for free (at least briefly) in order to see if there's a case worth pursuing. If there is a case, don't count on them taking it pro bono. Never know unless you ask though.
My best guess is that there's nothing to be done about it except the rejected options of vandalism or quitting. There's a slim (as in "invisible when turned sideways") chance that some local law might give you more to work with but that's for other nerds to figure out.