In the 1970s, AIGA and the U.S. Department of Transportation collected the most common and effective symbols used worldwide to help manage transportation information in public places.
These sure beat the written out "Don't Walk" signs on every street corner of major U.S. cities—positively inconsiderate of visitors from other countries or people who may be challenged in literacy for any number of reasons.
The symbols selected and adapted by AIGA and D.O.T take in to consideration the cultural differences and various interpretative abilities of the pubic, striving for clear, easy-to understand iconongraphy. Now that's considering the goal (public safety) and the end-user (a broad array of people.)
These are now available for download on AIGA's site.