Saiguan is the component brand of Ningbo Saiguan Bicycle Co. Ltd. based in Ningbo, just south of Shanghai. Eerily similar to SunRun (the two companies also have similar addresses), the company was founded in 1991 and claims to manufacture a mere 6 million rear derailleurs per year.
The top row, below, is a case of ‘spot the Shimano Tourney copy’. The bottom row is slightly more interesting.
Saiguan HG-08 2003?