"Der Berg ruft" (1938) is the title of a film by mountaineering pioneer Luis Trenker (yeah, we share the name).
The meaning is more or less "the mountains are calling" and the film is about mountain climbing and alpine skiing in the first place
Nowadays, this set phrase is pretty popular among tourists coming to Austria for skiing - mainly used by people who don't really know how to ski, however!
so the t-shirt design reads
*the mountains are calling - move away* (actually "piss off")