What does a flashing yellow arrow traffic signal mean?
Flashing yellow arrows have been introduced in the US recently to help ease congestion at intersections. This signal should be treated similar to a yield sign or a turn lane not controlled by its own traffic signal. If there is no oncoming traffic, you may make a left turn if it is safe to do so, but you must yield to any oncoming traffic and to any pedestrians in the crosswalk you would cross when turning.

Although laws vary regionally with regards to how bicycles are treated in traffic, in most cases a cyclist would handle this situation the same as any other vehicle. If there is no oncoming, you can make a left turn, but be wary of traffic coming the other way. It may be safer to wait if you don't have a full view of oncoming lanes (i.e. if there is a blind corner or low visibility), since it will take you longer to clear the intersection than a motorized vehicle, and drivers coming the other way will not be expecting a bicycle in the intersection during their green light cycle.

This animation from the Alaska DOT shows how the flashing yellow arrow sequence works: