The sounding or blowing of any horn or any signal device on any automobile, motorcycle, bus, or other vehicle while not in motion, except as a signal if another vehicle is approaching apparently out of control, or if in motion only as a danger signal; the creation by means of any signal of any reasonably loud or harsh sound; and the sounding of the device for any unnecessary or unreasonable period of time shall be prohibited.
Penalty, see § 94.99