I would bet it is a mark that was used during a refurbishment. http://forums.gunboards.com/showthre...912#post739912 another example of a lazy 8 on a Mosin, this time a Tula m44 on hex receiver.

One of the Ukrainian make PU replica scopes http://www.ebay.com/itm/RUSSIAN-MOSI...item231e4baf87 And another one. http://www.ebay.com/itm/SOVIET-RUSSI...item4166e86915

Polishing the receiver to me wouldn't be worth while. It would be a lot of work for not much in return. Could instead work on the trigger, and the bolt