In my experience, the AE term 'PSA' isn't used for security announcements at airports (e.g., report unattended luggage), only for educational or informative messages on (otherwise) commercial TV or radio.
Usually in the wee hours when a broadcast channel has been unable to sell an advertising slot (because most people are asleep and there is no good programming on), or sometimes now even during network evening news (because no one but senior citizens, and me, seems to watch that any more), the station will fill up the remaining time by airing an educational message, usually sponsored by a nonprofit organization or government agency.
As patman says, examples might include reminders about not driving drunk, securing children in car seats, staying up to date with vaccinations, supporting nonprofits that help at-risk children, suicide prevention, not littering, flu shots, checking on elderly neighbors during summer heat waves, not driving into flooded streets ('Turn around, don't drown') ...
NHK from Japan has a few really cute ones during its newscast about how to craft useful things in a time of emergency, like making leg coverings out of garbage bags and tape to wade in flood waters, or sandals out of cardboard while staying in an emergency shelter.
Some stations might also occasionally accept things like announcements of coming events for the community calendar under the general heading of PSA's, only airing them if they happen to have a little extra time.