It's been hinted but to make it explicit: we are in more difficult economic times than when you were hired. Maybe every new hire is getting less than back then, irrespective of gender. So, if you feel incredibly strongly about this, you as a minimum need to gather much more evidence before you can even be sure there is a problem. But you might be better just letting the people more directly concerned identify and address any problem that may exist for themselves - or are they inferior in some way that means you have to do it for them?
... and the next time someone leaves private correspondence in the open, cover it or turn it over without reading it, and tell them at your first opportunity. That way, maybe they'd pay you the same courtesy.