Do a Google Image search for “stop sign” and you’ll be blambasted with countless signs displaying a wide array of fonts used for the word, “STOP”.
The FHWA MUTCD has the final say. What’s the FHWA MUTCD? It’s the United States of Transportation Federal Highway Administration Manual on Uniform Traffic Control Devices. Now, doesn’t that sound official or what? I downloaded the 864 page FHWA MUTCD and my search couldn’t find any mention of an official font. Sadness.