Is it legal to hang ads to door knobs?

The legality of hanging ads on doorknobs varies by location and local ordinances. In many areas, it may be considered littering or trespassing if the property owner hasn't consented to the placement of such materials. Additionally, some municipalities have specific regulations regarding door-to-door advertising and solicitation. It's advisable to check local laws or homeowners' association rules before distributing ads in this manner.