If there is a car that has been sitting around your car for about 5 minutes before leaving, just keep an eye out. If you are able to get the license plate without leaving the house, get it. If they return, contact your local police department and let them know of the suspicious activity. Try not to let them know you see them, and do not confront them.
walk out of your house covered in red liquid carrying an axe covered in the same red liquid and a stuffed trash bag covered in it also. drag it to the curb and wave the axe at them kindly as if saying hello.
keep your face covered. they might be stalkers and they might be looking for you. As you walk out the house with your face covered, pretend you are trimming the garden, getting your mail, etc then, get the license plate number and the look of their face. if he/she comes more than 5 times, call the police or ask around to see if anyone knows the look of their face or license plate number.