Now this is just a guess, but they do use the Cyrillic alphabet in Bulgaria so the I'm thinking the lettering will be the same on a Russian or Bulgarian AKM. This is probably true for most of the ex-soviet states which produced them.
In fact, Cyrillic was even invented in Bulgaria according to wikipedia;
http://en.wikipedia.org/wiki/Cyrillic_script
Circle ten is definitely "Arsenal of Bulgaria". With the origins of Cyrillic coming from the Bulgarian empire, it's more of a case of Russian weapons having Bulgarian lettering on them. In fact, Russian everything has Bulgarian lettering on it.
But Cyrillic on your circle ten does not make it a Russian gun. Actually a lack of cyrillic would make it's Bulgy status questionable.
That help?
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