Achieving a solid die strike of the oval hallmark was a difficult task given the inconsistency of most obverse surfaces of Mint Of The United States At San Francisco silver ingots. You will see them in almost any alignment thinkable in an effort to strike the most surface but never before have I seen this approach.
The die was actually struck twice on this Type I oval hallmark, medium font with curved stem nines in 999.5 fineness. There is a slight "ridge" running down the center of the ingot from the trailing edge to the leading edge, (top to bottom). The hallmark die was first struck on the right side of this ridge and then struck again on the left side. With magnification you can see the actual overlap.
Very interesting and another first.