Generally speaking, bicyclists have the same rights as motorists while using public roadways. Therefore, you must give them the space that they need to get to their destination safely. If you see someone riding their bike on the road, it is a good idea to slow down and watch carefully for any signals that they may give.
A bicyclist is generally required to make a hand signal when changing lanes or making a turn. However, there is no guarantee that this will happen in a timely manner. Therefore, it is critical that you look for any indication that he or she is going to slow down, stop or make a lane change.
Ideally, you will slow down or stop when approaching a crosswalk or intersection. Doing so gives you an extra second or two to look for pedestrians who may be obscured by a vehicle or other large object.