On a recent road trip, I observed that all highway signs are the same design, font, colors, etc.
As a branding guy, I asked: Who makes them? Where are graphic standards?
The signs are published in a special section of Standard Highway Signs.
The contents of the 2012 Supplement incorporate new additions of signs and markings, with details for all signs and pavement markings, expanded sign design guidelines, and details for symbolic traffic and lane-control signal indications.
It's everything you'd expect in a combination of a brand standards guide and a government publication.
Click on the link to check it out at http://mutcd.fhwa.dot.gov