I have a mk 4 #1 U.S. property marked on the left side.
Its also on the reciever ring EK/SE_OS with a triangle
pointing up. The finish is green. Don't know if the
Finish is original but it looks lIke it might be or arsenal
refinish? Anyone recognize this mark?
I haven't been able to find anything about it.

As you know, all or most all, Savage made #4MK1*s are marked US Property; because we paid for them but gave them to England.
As for the other marks, IDK.
Green finish? Painted? Or green phosphate?

Green paint

British did that during rebuilds, I have had them like that.

It would be interesting to know who the brits sold it to after the rework.

Interterms, Century arms, Kleins, many others; they imported them by the literal ton in the 60s. I bought my first one in 1967, direct, before you had to have a license to order rifles. $24. A lot for a high school kid.
It was painted light yellow/green and was covered in cosmoline. My mother was convinced I had lost my mind.

Yep. Those were the good Ole days.

The recv'r ring markngs are most likely Greek Gov't from the info I've seen.
Or at least that's the best guess by a number of folks.

The EK/S usually looks like it was one separate stamping.
The E_ OS usually looks like another separate stamped mark. (The _ is underneath the E)

Some have speculated or interpreted that in part it abreviates to 'Training Rifle' in Greek.

A large number of #4 rifles were given to Greece after WW2. Then there was the Greek Civil War. The marking may have some connection there

I'd look for a plug in the chamber or a hole drilled into the chamber from below like some of the DP Enfields just to be sure.

That's all I remember. I was more into No1 rifles than the #4.
Mr Google may turn up something for you if you use this as search info.

The rifles is a shooter. Only thing is the muzzle is counter bored 5"!