Setup a motion sensitive video system to catch the idiots doing hit & runs. Video/photographic evidence is very handy in reporting hit and runs to the police. Probably won't cost you too much to get a decent system setup.
Unfortunately, not many people pay attention to playground zones in residential areas. Replacing the signs probably won't help. Getting the police to patrol the area will likely reduce the speeds, but won't protect your vehicle from the occasional bad driver.
Painting a large boulder like a car might be fun revenge though
Sorry to hear about your truck!