Hello, it's a ZK lens, marked Zorkii ... ZK stands for Zonnar Krasnogorskii. These were made with original Zeiss parts & optics, and assembled at the Krasnogorskii Mekanitcheskii Zavod - known as the "KMZ" plant. Consider that this is almost a 50/1.5 Zeiss Sonnar assembled in USSR from german parts. Doesn't means it's fully and only made with german parts though, and doesn't means the quality is that of a Zeiss lens, but it's a rarity. Other members will probably confirm and / or correct me.
This lens fstop ring has "ears" like the ZK and Zeiss lenses do. My later Jupiter-3 (50/1.5, evolved from the 50/1.5 ZK) doesn't have the ears, and the body of mine looks like if it is made with aluminium while the one depicted here seems of a more solid, heavier material. I say "seems", no one knows for sure until you hold it. It seems to be a genuine ZK.
By the way, I wonder what kind of "animal" has been "munching" on the filter mount thread 😉
Regards!
Max
