According to a press release from Upper Austrian state police, attention was drawn to the graffiti by visitors to the camp on Sunday.
A visitor complained to one of the employees that a felt pen and a sharp object had been used to draw and scratch four of the Nazi symbols on the walls of the former laundry of the camp, as well as in the bunker area.
The word Hitler was also written on the walls. Police believe that the vandalism was carried out during opening hours on the previous day, as visitors don't have access outside of those times.
Some 200,000 people, around a quarter of them Jewish, from 40 nations were incarcerated at Mauthausen, set in rolling hills just north of the Danube river near Linz, where Hitler went to school.
Around 90,000 didn't make it, perishing in back-breaking labour in granite quarries from malnourishment, disease — or shot by the guards, hanged, throttled, beaten to a pulp or gassed.