The sign, which has been in the window of Mattsons Foto & Video for eight years, reads: "Expensive cameras are not left in the store overnight".
It was not until recently that an inhabitant of the southern city decided to report store owner Ulf Ögge to the authorities for being anti-Polish.
But Ögge has said he does not intend removing the sign unless ordered to do so by the ombudsman.
"Eight years ago I had three break-ins in a short space of time. The thieves drove a car through the entrance. When I was in court it turned out that all the perpetrators were Poles and they weren't able to speak Swedish or English. A Polish friend of mine helped me to write the sign," he told Metro.
DO's legal expert Per Holfve, who has just received Ögge's official response, said it would take some time before a decision was reached.
"We are looking into whether this is a form of harassment," he said.