The classic sign was a one-sided, wall-mounted panel. The earliest are convex and often slightly in relief, more exaggeratedly so in the types in lithographed tin.
The forms are for the most part regular -rectangles, squares, and circles- though there is no lack of signs formed in elaborate ways.
In some rare cases (one being that of Mobil’s flying horse) the modeling is so accentuated and the relief so deep that the subject represented acquires a sculptural concreteness.
Often, especially in America, the sign was detached from the wall and mounted on a stand, pedestal or pole, inserted into the space of the service station, making it yet more effective a means of attraction and prefiguring the giant signs of today.
In this case, both faces would be illustrated, or the supportwould join two separate signs back-to-back.
A separate discussion is merited by another genre of enameled sign, used in Italy not at the sales locus but directly at the roadside: street signs, indications of place, and announcements of services installed at highway exit ramps by the Touring Club, but paid for, totally or in part, by the gas and oil producers who, in exchange, added their trademark to the bottom.