No vehicle shall be allowed to block any alley, street, or sidewalk, except for vehicles loading and unloading, and for emergency vehicles when such vehicles are being used in the line of duty. A vehicle shall be presumed to be loading or unloading when its emergency flashers are on and a sign labeled "loading" is placed in plain view on the dashboard. No vehicle loading shall be allowed to fully block a city street for more than five (5) minutes. (2008 Code § 17-128)