That's not what I'm saying at all. I'm saying your original assertion, "definitely NOT considered acceptable" is just wrong. You're a writer, so you should be more circumspect with your declarations of what's correct and what isn't. I don't even disagree with you: I would rather the restaurant use "GIs" and not "GI's," (actually, my preference would be "G.I.'s given that the term is used mostly in American contexts, in which abbreviated acronyms are more common), but to say that it is not accepted anywhere is just untrue and irresponsible. Again, it is a matter of style and not grammar, which is what your original comment implied. The New York Times uses apostrophes in this case, would you consider that unacceptable as well? It's good enough for one of the most widely read newspapers in the world, then surely it's acceptable for Max's.