Doesn't matter if you have a tow sign or not. Due to a major issue with predatory tow practices in Philadelphia, a car must be ticketed to be towed. No tow company will touch a private tow request like this without a ticket
Source: had a paid off street parking spot with signs and still had to call police to ticket
Unfortunately, you have to keep calling 911 until a cop shows up to ticket it. Then you can have it towed. When this happens to my driveway, we do a cursory knock on neighbors' doors to see if we can find the person first.
trashpandarevolution t1_j1sovhv wrote
Call 911, repeatedly and early into the situation. They will eventually ticket and then you can tow.
Be ruthless. Put up a big ugly sign. Illegally paint your curb cut yellow. Do whatcha gotta do and stop worrying