from PWN online dictionary:
tirówka pogard. «prostytutka szukająca klientów wśród kierowców TIR-ów» [pejorative «a prostitute looking for clients among TIR drivers»
TIR = "Transports Internationaux Routiers" ("International Road Transport") are simply those big trucks, whose drivers spend hours (or days) in the car and tirówka (easy to find at the most important roads, highways, parkings or motels) provide them with some "entartainment"