Well, maybe to you and me. To the average driver, I'd wager it equals "emergency vehicle".

Which is why now that lights are getting brighter motorists are pulling over. It's also why blinking lights are illegal in CA (front or rear, if I recall--and it's not generally enforced, no).

Stories about cars pulling over are funny, but they're going to lead to increased resentment of bicyclists if something is not done.