RS Prussia Mark a Fake?

I won this at a very reputable auction house, but unless I am mistaken, I think it might be a fake. Can anyone tell me if this is possibly a real mark of RS Prussia? Every "red mark" I find looks just like this but has "Prussia" written under the mark.

Thanks!

 

Country of origin wasn't required on items imported into the USA until 1890, and may not have been used on things meant for sale within the country of origin at all until a lot later. From a quick glance in my Kovels, the company went into business in the 1870s, and this design looks to be 1880s. If it is, the country mark wouldn't have been in use yet.

 

In my opinion it's a fake mark. It's too large and the colors are too faint. Additionally, the mold doesn't look right especially on the cup handles. There is a very good RS Prussia group on Facebook that may be able to confirm my opinion.