No, the MK probably stands for "Mästerlig Kvalite", translated it would mean something like Superb Quality.
I've found this referenced around Swedish historical societies online.
From what I have found suggested, the BK would be Bästa Kvalite", thranslates to something like Best quality.
The RK is harder to find anything on out there
This thread provides a bit more about the subject:
http://straightrazorpalace.com/show-...questions.html