Mark
In recent years, I've been in a similar situation with car damage.
And as you point out, with no consequences, not only do they get away with it, they get the reinforcement that they can continue and get away with it.
With some consideration, I had ideas on who had done it, but nothing more - I'd not had any run-ins, disagreements or bad feeling (that I'm aware of) with anybody.
What I would suggest is reporting every bit of damage, when it occurs, to the police. If they come out to have a look, or chat to you, then their presence may make the perpetrator nervous or aware that more than your attention has been drawn. Plus if it happens more than once, and the police have to record something, after a bit, they (the police) may get a bit tired of it.
When I reported a couple of incidents of vandalism to the police, I didn't mention any suspicions - because they were merely that, I had no proof, or even anything firm. And tipping the wink to somebody who may become aware that you have, may cause further problems.
I decided that other than that, I'd do nothing more about it - I had nothing other than suspicions, and any retaliation can just escalate - and in that scenario, you have to consider who's got most to lose.
I did find it frustrating, because whoever did it, got away with it, and presumably viewed their behaviour as being reinforced - whether it was to discourage us from parking in certain places, or simply because somebody didn't like us, I'm not sure. I bought a cheap runaround car that I wasn't bothered about being damaged, and only that was parked near our house for a few months.
I don't really know what the answer is - whether you have clear ideas on who's done it, or not. I agree that it's frustrating, lose-lose, yet you feel compelled to do something about it.
