PAO was a department, division, or position within Starfleet's Fleet Operations Center on Earth.
In January of 2155, Starfleet officers J. Van Over and D. Sperber worked in (or as) PAO. (ENT: "Demons" set artwork)
PAO was seen on directory listings seen on the set of "Demons".
, like many of the other divisions, departments, or positions on the listing, is a reference to NASA
terminology, in this case, the "Public Affairs Officer".