Just found this forum, and the award document for Wilhelm-Richard Rossiger for his RK.
For those who may not know, I have researched Erprobungsgruppe 210 since 1980, and have written the history of that unit.
During my researches I met the Staffelkapitän of 3./Erpr. Gr. 210, (Oberleutnant) Otto Hintze, several times at his house in Munich. I was able to see his RK, and the award document that went with it. In the early part of the war, Hitler personally signed the RK award citations. It was only later, when there were a lot more RK awards, that he no longer signed the individual awards.
So my view from looking closely at this one, and comparing it with the photographs I have of Otto Hintze's citation, is that it is the genuine article. It would be useful if the original poster could cite details of where the article is up for auction. That may then provide information on the provenance of the item itself.
Hope this helps.
Edit: Here's a scan of the photo of Otto Hintze's citation:
I was able to hold it, and examine it in great detail. Definitely not a stamp for the signature.