It's funny how things like this only look like another object once someone mentions it. For example, when my step kids were little, they used to constantly ask about the "underwear" signs posted all over the place. Couldn't figure out what they were talking about, until I had them point it out sitting at a red light.

The traffic lights have stop signs that are folded down, and get unfolded when there are problems with the signals. So the bottom half of a white octagon does look like a pair of briefs.