Bicycles may be operated upon the public sidewalks in a careful and prudent manner, except where signs are erected to prohibit riding on the sidewalk, and at a rate of speed not exceeding eight miles per hour. Every person lawfully operating a bicycle upon a public sidewalk, when approaching a pedestrian or a vehicle occupied by a child under the age of 16 years, shall either dismount or give a clear right-of-way to the full extent of such sidewalk to such pedestrian or child and, in overtaking such pedestrian or child, shall give an audible signal before passing.