Call the police and tell them you smelled some pretty funky stuff coming from their camp. Drugs or something. And people were making weird noises. Nothing's better than a middle-of-the-night search by the vigilant police.
Also, if they are out camping and really think seeing a rifle is bad, they have good odds of having something on them. Not that I have anything against what they most likely have... but they should be made to realize that currently, guns are legal and that is not.
ETA: as the poster below me points out, this is not something you should do if you actually did not smell some pretty funky stuff coming from their camp, or hear weird noises, sorry about that, I made some incorrect assumptions based on my own previous experiences of what people who are out camping do.