As some of you may know, I've been studying and researching #2 RRBs for a while. I've examined well over 150 of them.  This is the only one I've ever seen with this type of patent markings.   

This seems to be an oddity that occurred very early in production.  The very first rifles from late 1872 were known as Gem rifles.  They have company and patent dates on the upper tang.  From my research, the highest Gem serial number I’ve seen so far is 206.  By far the most common patent date markings are the five line (seven patent dates) on the forward end of the left side of the receiver.  The lowest serial number I have for this type is 538.

But between these two marking types is what seems to be an rare variant with company name and patent dates along the top edge of the left side of the receiver.  This is very similar, but not exactly the same as the M1871 rolling block pistol.  So somewhere between serial number 206 and 538 (311 rifles) they stamped them along the top, left edge.  I know of only one rifle like this; serial number 371.  It is now in my collection.

So why did they do this?  Maybe it was an interim solution while the dies where being made to stamp the later 5 line markings.  But why not just continue the top tang Gem style markings?  One could speculate that they wanted to clear the tang in order to drill and tap for a tang sight. But tang sights were uncommon in this time period.  The lowest recorded #2 serial number of a drilled and tapped tang rifle I have is 6877.  So I don’t know the answer. Research continues....
   

😲

Awesome! I'm still looking for another one.