No person shall operate, play, or permit the operation or playing of any radio, television, phonograph, drum, musical instrument, sound amplifier, or similar device which produces, reproduces, or amplifies sound in any place of public entertainment at a sound level greater than 90 dBa as read by the slow response on a sound level meter at any point therein that is normally occupied by a customer, unless a conspicuous and legible sign is located outside such place, near each public entrance, stating: Warning: Sound Levels Within May Cause Permanent Hearing Impairment.