The United States Flag Code says, in part, "The flag should never be used for any advertising purpose. It should not be embroidered, printed, or otherwise impressed on such articles as cushions, handkerchiefs, napkins, boxes, or anything intended to be discarded after temporary use. Advertising signs should not be attached to the staff or halyard."
As the flag should not be displayed at night, whoever places it at a curb should take it down at sunset.
Also, whoever places these flags should go through the neighborhoods where they placed them, removing any that they find in the street or gutter and dispose of them properly. According to the Flag Code, any American flag that is worn, damaged or tattered beyond repair should be retired in a respectful and dignified manner. The preferred method is burning. The Veterans of Foreign Wars, American Legion, Boy Scouts of America, Girl Scouts of America, the military and other organizations regularly conduct dignified flag-burning ceremonies.
Almost all homes in my neighborhood get flags placed curbside by a local real estate company (btw, there are several RE companies more local than this one). Although I'd prefer not to receive one, I'm puzzled as to why, for the past several years, no flags are placed at homes on the block where I live. I'm told another RE agent lives here, but I don't think that is correct. I also fail to see why that should matter.