This is a sign on the counter of a diner in The Grapes of Wrath.

You can guess what it means. Or, failing that, buy me a drink, and I'll tell you.

Anyway, is this a common gag in the U.S of A?

Some would have it IITYWYBMAD .

Sure, but in The Grapes of Wrath (as you'd know if you'd read it) it is IITYWUBAD? because the sign is put there by the management who want the patrons to buy drinks for themselves and take the profit. Like freaking duh.

re: Like freaking duh.

not really freaking d'oh, but something like it..
like duh.

or like dumb

or..

Like, you know, like, what, like, i am saying, like--
freaking duh.

how do you spell airraid backward?