At a news conference in Krakow Monday, police said the theft was a criminal act, and that the intent of the five "was undoubtedly robbery-related."
Police said Sunday they found the sign cut into three pieces in northern Poland near the home of the thieves, who underwent questioning in Krakow.
The sign with three words in German, "Arbeit macht frei" is one of the most chilling symbols of the Holocaust. The sign stretched across the two gates at the entrance to Auschwitz.
The Nazis killed more than 1 million people there before Soviet troops liberated the camp 65 years ago next month.
Most of those killed there were Jews. Other victims included Roma Gypsies, Poles, and Soviet prisoners of war.
Auschwitz is now a museum.
Some information for this report was provided by AP, AFP and Reuters.