The earliest forms of hand painted communication on vehicles by trained sign artists always employed "Who-What-Where" and in context with a proper font, being complimentary to the message and overall layout. A sign does not function with just a font selection alone, but should be aesthetically balanced with correct positive/negative ratios, and correct letter size priorities of the message. Any sign having those considerations could easily be recognized as one done by a trained professional, or a gifted individual, and recognized by one who knows and appreciates the difference.
In the past there were many sign guys who would just dip their brush, and move it around till it looked like something to them. They were the ones, in demand today by Americana antique collectors, valued only by their current accepted value rather than an appreciation for proper sign lettering. Again reflecting individual and early American beginnings.
Today's world of computerization offers a similar antiquated approach for business opportunities. As an example, anyone may buy sign software for their computer, and presto, your in the sign business by signing on the dotted line. No artistic or sign experience necessary. This method is just a continuation of the self-taught method reflected through a customer who doesn't know the difference, or doesn't care. This has also changed the application and interpretation of a sign writer from "Artist" to "Vendor".
Established sign companies are rated by the customers they keep!