While researching the photo and the shoulder patch, the black cat reminded me of the 13th Infantry Division's shoulder patch which also prominently featured a black cat as part of its design. Here the 13th Infantry Division's black cat patch is compared to the above 13th Engineer Regiment's black cat patch.        

it's a box that I have and not a button

Larger views of the "castle and cat" shoulder patches. Note that the numeral "13" shown in the center of the patch in the first photo has been washed out in both of the below images. I have posted the first photo again, showing the numeral "13" for comparison.    

Wow, i missed this one big time! Very nice looking RIA!  You might look for the bolt steel lot code at the front of the safety lug, it could be a D1 or a C13. If you don't find anything there, the bolt may have been replaced at some point. I don't think the engraved S/N on the bolt means it's a Greek returned rifle, to me it indicates that it was marked just to keep that bolt with that rifle for correct headspace. I would say that the stock has been refinished by the faint P proofmark, is there any evidence of a cartouche on the stock?  Most RIA rifles of that era had the CN(Conrad Nelson) stamp.  You also have a very nice SA bayonet and early scabbard. An early sling, front sight cover and a cleaning kit would complete this good looking outfit. Keep looking! Thanks for showing this.     Steve

I do not think it is military. This is on EBay.

Closer looks at the soldier    

Before I go any further, I should post the two photos that I obtained showing the mystery engineer patch with a black cat.    

It's difficult to see, but the numeral "13" appears above the castle on the collar disc. The same numeral also appears in the center of the shoulder patch.   Most of us know that the 13th Engineer Regiment in the AEF was a light railway regiment that operated under the command of the AEF Armies and Corps. It was not a part of any of the AEF infantry Divisions. The 13th Railway Engineer Regiment had a well-known shoulder patch design of its own, which is shown below, and looks nothing like the shoulder patch worn by the unidentified engineer in the above photo.    

I live not too far from this park and when I saw this WWII plane I had to stop and get out and take a look at it.  The information on the various plaques were very interesting as well as the wonderful restoration to WWII looks for this C-47 which most likely saw action.   Note:  I took these photos and that's my Jeep in the background.                                              

I recently purchased three photographs of an unnamed WW I American doughboy wearing an as yet, unidentified shoulder patch.    Two of the images show him in the same uniform, while in the third he is wearing civilian garb.   There was also a larger portrait photograph of the same soldier in the same uniform showing the shoulder patch in greater detail. Sadly, the seller kept this photograph for his personal collection. As mentioned above, I was able to obtain the remaining three photographs.   I'll start with the seller's image because it shows more detail.