Sometimes they use this type of light:

This type of light is usually a steady blue. But sometimes they use this light:

This type of light is a strobe blue. It is more common and is seen better, therefore is the best option. So my guess is that since it flashes, it is the strobe.
*EDIT: I also just learned from the 3M website that these are also used for transit busses. Has anyone known of this, seen it happen, or know if it is selling well?