A long time ago I bicycled across the U.S., and I came across a guy who rode his bike with a pink skirt and blond "pony tails" attached to his helmet (pony tails were not terribly convincing close up, but from a car, they looked "real"). He said motorists would give him considerably more room. I briefly considered doing the same but was too lazy. Also I had this crazy idea that I was a guy back then. :)
Also came a across another couple from Germany. They rigged these detachable, small triangular red flags to their bikes that poked out into traffic maybe a foot and a half. They also said motorists gave them considerably more room.