While walking back from my weekly ultimate frisbee game on the Esplanade, I noticed an odd sign suspended above Storrow Drive Westbound in Boston. The large road sign was hanging below a bridge and read "Reverse Curve." After thinking about it, I realized I had no idea what this meant.

Dictionary.com provides this illuminating definition: "Reverse curve (Railways), a curve like the letter S, formed of two curves bending in opposite directions."

Another one for road signs we do not understand.