Hate to be a punk about it but maybe someone didn't like that you were breaking the law. City ordinance doesn't allow on street parking for more than 24 hours at a time. Use your garage or be more considerate and don't break the law. In fact you should probably review the city code and ensure you aren't violating any other laws. The ones that bug me that I see all the time are trash cans, parking on the wrongs side of the street, jay walking, parking too far from the curb, unleashed dogs... I would never do anything other than report you to police but apparently other neighbors aren't so nice.