Thirty years ago, I used to see folks riding with a three foot long orange plastic rod that protruded from their bikes to their left. Those rods had a little orange flag on the end. The whole rod/flag deal probably weighed less than four ounces or so. Yet, for some reason, motorists were greatly afraid of getting near those rods. They would swing their vehicles six feet to the left to make sure those rods were far from their vehicle. I was always amazed by drivers over-reaction to those little rods.
In Houston, a "three foot" tee-shirt would simply encourage the guys in pickups trucks to go around the block for a second attempt, if they failed to hit you with their passenger door mirror on their first attempt.