The stamp above is genuine and its trade mark is: OFF CENTERED. The length of the black frame (outside measure) is 29.50 mm. Source: Pertti Hujala
There are many forgeries about the inverted center Viking 5 Mk. The white paper forgeries - as is this one below - eventually belong to the early production. If you are not careful, you will be deceived easily with this quality forgery.The length of the black frame below is 30.23 mm. That is a forgery, printed on quite white paper and it is "too well centered".
The pair of 5Mk Vikings below is a total forgery. It is also printed on white paper and it is "too well centered".
The above pair belongs to this letter below. The whole object is the total forgery, including cancellations. Obs: the handbook says: Pääskula post-office was opened 3.9.1925 and this postmark cancellation is from January, 1921. The name Pääskyla is quite known with this kind of forgeries.