If you want to send a card that says SEASON’S GREETINGS, check the card to make certain that apostrophe is in place. The greetings belong to the season—one season. I have seen cards printed with no apostrophe and others printed with an apostrophe after the final S in SEASONS. You are not sending greetings for multiple seasons.
People go crazy with apostrophes. When they see a final S, they reach into their bulging apostrophe pocket and hurl one at the word. That’s why you will see signs in grocery stores telling you to buy APPLE’S, RADISHES’ AND PASTA’S. None of those words is possessive; they are merely plurals. I saw a sign painted on the side of a truck that bragged the company had ‘The Best Plumber’s in Town.”
If I could get $5 for every missing or misplaced apostrophe, I would be a rich woman in two weeks.