Additional Markings on Mod 60 Crane

[Ron Thompson]

A friend purchased a S&W Mod 60 No Dash. He asked me what a specific marking on the crane meant. Below the standard number marking to identify parts was the marking E3 in letters about four times the size of the standard numbers. I have no idea what the marking is. Can someone help?
Thanks

 

[H Richard]

I believe that is an inspector or fitter's mark.

 

[Ron Thompson]

Thank you. That was my guess but I wanted confirmation.