what does 1 troy oz..999 F.S.74PHM mean?

Answer 1

PHM stands for Purity Hallmark. So silver which is .999 is 99.9% pure and it's guaranteed by the PHM.

Answer 2

The F.S. part of the equation stands for fine silver. .999 is how much of the bar is made of silver. The PM stands for purity mark. On each bar, there is a symbol that shows that list of numbers u listed in the question. I don't know how u got PHM, it is really PM.

this site has info on what a troy ounce is:

http://en.wikipedia.org/wiki/Troy_weight

This is a site where they sell silver:

http://lynncoins.com/bars.htm

It includes a that string of numbers and letters you said.