"Mad. Ave." is an abbreviation, but it's also a comment on the mad, mad, mad, mad world of advertising.
11 October 1957, New York Times, pg. 45:
Advertising: Life on Mad. Ave.
by H. T. Elmo
New York: Ace Books
(Cartoons about the advertising industry - ed.)
4 October 1970, Washington Post, pg. 242:
...as an advertising copywriter in the New York jungle. His wife and he lose contact spiritually, and by the end Fitzie has to choose between saving his marriage and his self-respect (his soul?) and further triumphs on Mad Ave.