What is the correct way to define an acronym when its first appearance is plural? [closed]

Solution 1:

I'm going to disagree with RyeBread here (sorry) -- if the acronym is a normal one in all caps, and the plural is given with a lowercase s, as in your ATMs, then your option 3 is correct - the change of case distinguishes the s from the ATM, avoiding confusion, while putting the singular form in brackets next to a plural makes it look like the singular acronym is equivalent to the plural long form. An example from my field: High-electron-mobility transistors (HEMTs), though personally I would have spelt out the long-form with initial caps. Now with the example this is too long for a comment.

Solution 2:

My opinion is that the correct plural is ATMs which leaves room for an ATM to signal possession with an apostrophe, i.e. "Hey, this ATM's touch screen is broken."