i have had this happen to me with my rear bumper, one day while out shopping, walked back to my car and noticed straight away the little circle tow hook thing was popped out. lucky there wasnt much damage and my bumper already had scratches on it from a previous hit(i knew who had done that one) and yeah no note or anything.
im contemplating getting a tow bar put on my car purely for protection. if someone hits me from behind its gona do more damage to them then me

im a big believer in karma when it comes to cars! so hopefully whoever did this to u gets what they deserve.