I blogged about this item and how rare it is. At the end of the post I asked the readers to provide scans if the own one of those. So far I got several mails with scans but no genuine one. Here is a current example which represents the mailings I received.
Both perforated stamps are forged, the unperforated one is genuine. While there is variation in the general appearance (more or less clean) of the genuine print, here are some of the most easy to spot characteristics for genuine or forged.
The typical features of this forgery are the gap at the and of the vertical lines (upper arrow) and the unclean border frame (lower arrow).
The most prominent secret mark of the genuine print is this small downward stroke between the vertical lines (see arrow).
I am in full agreement with Stephan. However I consider secret marks as not secret but the failure to clean up the design prior to forming the printing stone. This is a general comment to all Russian issues. Never the less they do enable genuine items to be identified.