
The above example is a very common evil. I personally believe people do it to differentiate the "S" from the rest of the acronym (though I think that writing a lower case "s" solves that problem, as demonstrated in this post's title), while another argument offered to me once is that it's actually intended as an apostrophe of omission. I disagree with that analysis; in fact, the relevant Wikipedia entry only mentions the acronym scenario in terms of plural forming and not to show omission, so the internet agrees with me! I suppose you could argue that an acronym is a form of abbreviation, but I can't be bothered to go there right now because I think that argument would be a stretch, and anyway, in my oh-so vaunted opinion, the above example is just plain incorrect.