If you don't already know the latitude/longitude coordinates of the tower
you can find it on a mapping site like topozone.com then look up the lat/lon
on the FCC database and see what transmitters are licensed there.
They could be for a lot of things. If they are pointed up at satellites they
could be used for one of the nationwide paging services.
If they are pointed at the horizon they could be point to point links for
for whatever base stations, cell sites, etc. are on the tower.
The picture isn't good enough for me to see exactly what kind of dishes they
are.