I found it at the flea market during my last stay in Poland. According to NIA, it comes from North Korea http://www.nia.org/general/pifous/logos/makers/korea.htm. An interesting specimen from quite an unusual country, next to the D.P.R.K sign, there is a poorly visible number 28 marked with a red circle in the second picture. If someone has more information about this insulator I will be grateful for sharing this with me.