Columbia subject headings:
Advertisers--Canada--Directories.
Advertisers--Directories.
Advertisers--United States--Directories.
Harvard subject headings:
Advertisers--Canada--Directories.
Advertisers--United States--Directories.
Advertising agencies--Directories.
Princeton subject headings:
Advertisers--Canada--Directories.
Advertisers--Directories.
Advertisers--United States--Directories.
Directories.