Fs can mean For Sale, Full Size. Do you mean SF? Square Footage.
In the personal ads that I have seen, LOS means Lost or Stolen.
Androgynous
Long Term RelationshipLTR in personal ads means long term relationship.
professional
water sports
OHAC mean in Relationship
In Search Of
friends with benefits.
Pay to play
Bareback, or no condom
"short Message service" in other words text. It's not exclusive to personal ads.