Diamond CD aka ООО "Даймонд СД" is pirate company, owner of Diamond Sound label. On some releases it appears as a label itself.
Some releases contain the following text on artwork:
Лицензионное соглашение между РАО и ООО "Даймонд СД" № 2141/М3-97
"2141/М3-97" is the ID of the license agreement between РАО (Russian Authors' Society) and the label, which allowed the label to release CDs for the Russian market. But it was reported that actually no money were paid to the Western rights owners, so this label's releases should be considered Unofficial.
The company was working on the markets of Russia and Ukraine in the '90s. CDs were probably manufactured there or in Bulgaria.