I would blame this one on DDG, actually. PSA is an incredibly common acronym for public service announcement. Wherever DDG sources acronyms for might also be assuming people just know it. Try wiktionary or Wikipedia disambiguation pages for acronyms when they don't show up in search, I can often find them there.
Sorry to see this downvoted, I think it's a common courtesy to spell out acronyms on first use, no matter how widely understood one believes them to be.
I think that's because most people consider this requires unjustified. Do you think similarly about expanding acronyms like SSH, CLI, HTTP, HN, FYI, USD, US, EU, PKI? Why/why not?
duckduckgo just says PSA is Prostate specific antigen. What did you mean?