Thermo, You did the right thing in reacting to a potentially dangerous situation. For that, you should be commended. However, you probably would have been better off just calling it in to the PD. Don't know about your department, but around here they would have been all over it and it would have been dealt with. At minimum, a BOLO would be issued to cars in the area.
I also agree with Dood, why are you wasting time arguing with a potted plant?