Columbia subject headings:
Postcards--United States.
United States--Pictorial works.
United States--Social life and customs--20th century--Pictorial works.
Harvard subject headings:
Diners (Restaurants)--United States--History--20th century.
Motels--United States--History--20th century.
Postcards--United States--History--20th century.
Postcards--United States.
Service stations--United States--History--20th century.
Tourist camps, hostels, etc.--United States--History--20th century.
United States--Pictorial works.
United States--Social life and customs--20th century--Pictorial works.
Princeton subject headings:
Postcards--United States.
United States--Description and travel.
United States--Pictorial works.
United States--Social life and customs--20th century--Pictorial works.