Towing Issues: Resident/Homeowner Towing, threatening note, residential block

Question
I live in Denver, Colorado.  Most of the parking available in my neighborhood for my residence and my work is street parking.  I parked my car on a residential block for less than 12 hours.  The only posted parking restrictions were for street sweeping on Tuesdays, and it was Saturday.  I was not blocking a driveway or entrance.  However, I recieved a threatening note on my car from a homeowner/resident to have my car towed if I parked in front of their house for "all day" again.  This is not the first issue I have had in the area with residents claiming that I am parking in "their spot."
Does private property extend into street parking?
Is it legal in Denver, CO for a homeowner to tow a car from the street if there are no violations of posted signs and the vehicle was left for less than 12 hours and not over night?

Answer
No, the only ones who can tow vehicles legally from "PUBLIC STREETS" are the local police departments...

That being said, if you live in a "HOME OWNER ASSOCIATION" development then the HOA does have some rights and can have vehicles towed off the streets if they break the rules - covenants..

Some people just think that the street is their own property and that the parking is reserved for just them... Sad but true fact...