Hard to say, Mike. I vaguely remember back in the fifties and sixties that this phrase was used in social circles to imply exclusivity. It might have even stemmed from an ad campaign from the era. But, when you put these two mags side-by-side it's hard to ignore the similarity, isn't it?
Yes, it's not just the words ("For Men Only" "For Monsters Only"), but that in combination with the stacked words with the top and bottom ones smaller and centered. (The first letter of "Monsters" is larger, anyway.)