But if you have it, and an officer asks for it is another story. To my knowledge you do NOT have to present it, but you can NOT say you do not have ID when you do. What the officer is suppose to do is take you to the local Magistrate District Judge and charge you for whatever crime you did under whatever name they have for you. Remember you do NOT have to tell the officer ANYTHING, but if you do it must be the truth.
One last comment, under Pennsylvania you can ride a bicycle on the Sidewalks except in business areas. Until a few years ago the law forbade ALL riding on Sidewalks but the legislature took notice of the fact many people did ride on Sidewalks and changed the law. THis was part of the change that also dropped the requirements that if a bike trail was next to a roadway, bicycle had to go on the bike trail. That is NO longer the law, if they is a bike trail next to a road the bike can use EITHER. The reason for this came out of an accident about 10-15 years ago on Allegheny's County South Park Bicycle Trail. People were walking on the trail blocking a speeding bicyclist who had been told to use the bike trail not the adjacent Corrigan Drive. If I remember right two people died because of the Accident do to the bike path NOT being designed for bikes going over 10 mph, and the cyclist going about 20. The Cyclist testified that he only went on the trail after an Officer told him to use the trail not the road (Yes the County paid an undisclosed settlement to the people who died). Corrigan Drive was flat roadway, while the bike trail went up and down the adjacent hillside with curves and hills that reduced sight distances AND provided fast speeds for short distances to un-experienced cyclists.
As a result of that Accident the Bicycle Code for Pennsylvania was changed, first bicycles are no longer required to go on a bike trail if the trail is next to a road AND people were permitted to ride bicycle on Sidewalks except in Business Districts.
Pennsylvania Bike Laws:
http://www.dot.state.pa.us/BIKE/WEB/bikelaws.htm