As I’ve mentioned before, an acronym is not a synonym for an abbreviation. All acronyms are abbreviations, but not all abbreviations are acronyms.
NASA is an acronym—because we pronounce it as a word.
PIN is also an acronym. (Don’t say “PIN number.” That’s redundant.)
USA is not an acronym because we don’t pronounce it as a word; we say each letter.
To make acronyms plural, just add a lowercase s: All vehicles have PINs. You don’t need an apostrophe before that s. We do write about the Oakland A’s, only because it would look like the word “As” if we didn’t.