I was able to deduce what PSAs seem to be (in the way of 'hey people, this is another VERY IMPORTANT THING we want you to keep in mind') but I could not find what the supposed acronym stands for.
Public Service Announcement. http://www.youtube.com/watch?v=yFkzWSFW70M
It also could be:
- Please See Attached
- Personal Service Assistant
- Proxy Signalling Agent