"Just use an open standard that already exists!"
Based on AIGA's free symbol set for public transportation - Bleached color version of the "Arriving and departing flights" symbol".
From AIGA web site:
"...The complete set of passenger/pedestrian symbols developed by AIGA is now available free of charge. The system of 50 symbol signs was designed for use at the crossroads of modern life: in airports and other transportation hubs and at large international events. Produced through a collaboration between the AIGA and the U.S. Department of Transportation, they are an example of how public-minded designers can address a universal communication need."