Trans States actually started as Resort Air. At that time they flew a lot of people down to the Lodge of the Four Seasons on the Lake of the Ozarks. Most of those people were waterskiers. The 3 letter identifier for TSA is LOF after the Lodge of the Four Seasons.
I work for a charter company and we use a call sign, to my understanding, check this out with your fsdo, its all paperwork.
we registered our 3letter ident with our aircraft N #'s and changed them to UEJ 500 ;UEJ 600 ETC....so when center sees that on the screen they should know it is us...sorta..we get called everything but our callsign except when we are it our home area center. (we only have 13 airplanes, so unless we go to the same places alot, they have no clue who we are)