Some of the next boxes we will be getting into, "I" through "L", are pretty light; not much to be had in the 5 oz class throughout these and you will see that the overall lists for each are short as well. So into the "I" box.
Pictured first two with similar initials; IPM. The top example from International Precious Metals, Las Vegas, NV; the lower, Intermountain Precious Metals out of Idaho.
Next ICI, a fairly common hallmark but no other information; second, International Vaults Refining, one of the more elaborately hallmarked ingots; and third, IRC, International Recovery Company.