I've heard it's from the Polish, smok (or something like that).


Here's what AHD4 has to say about it:

http://www.bartleby.com/61/84/S0138400.html

BTW, I'm sticking with John Doe, at least until something better comes along. I don't think our Sam Spade is necessarily gonna use a military term unless some point has been made of his having been in recently.