What's a safer alternative to a flag for marking special bikes?
Some local recumbent users have a different style flag on their bikes rather than the rectangle or the pennant.  I couldn't find a photo online, but the flag is about a 1~1.5 meters tall, and the poll runs up the whole length of it.  It is then about a half meter wide.  There is very little flapping around and nothing loose to blow in faces and get tangled up.  I came across them driving so I can say they make you visible.  I have seen businesses use them before for advertising signs in windy locations.

Here is a image from Wikipedia.  It is called a vertical flag on it, the type I'm describing is 3.  (image credit)