Numrich sell the stamps and their eagle is looking over its right shoulder :
Numrich Gun Parts Corp. - The World's Largest Supplier of Firearms Parts and Accessories
Hand Stamp, GermanNazi Eagle - Use On Metal Wood Or Leather Surfaces.
On the MG42 forum they are discussing them as well :
"Look at the pretty Numrich Birdies ! !
Of course there are stamps that people use to make fraudulent k98 rifles. One of the collectors on gunboards.com has a huge collection of the stamps he got from Europe. He does not hump rifles with them, he just collects the stamps (and rifles too). the Numrich stamps are far enough away from the original that they can be spotted by an experienced k98 collector."