 I thank Tamar Szabó Gendler, Michael Glanzberg, Tamás Mihálydeák, and Jason Stanley for their comments. I am especially grateful to Daniel Rothschild for catching an error and for suggesting the repair in the preliminary draft of  section 2.  The entry relies at many places on Szabó, 2000a. Traffic sign images are from the  Manual of Traffic Signs,  by  Richard C. Moeur.  