The O & S are mintmarks. The was no P mintmark for the 1901, 1882,
and 1879 silver dollars. This link might help...

http://www.coinpage.com/glossary.php?search=mintmark



"Queen of Squishies" wrote in message link.net...
At the top of my little box was the silver dollars so I pulled those out
first and started looking around at some of the links that were offered. I
have three - 1901, 1882, and 1879. How do I know if something is a P, an
O, or an S? What's that all about?

Karen,
making cents in IL