You guys know the waypoints you see indicating a party/team friend or your house or even your body when you die? Nice, isn't it?
Now how about make possible to players create their own waypoints? I'd love it and I know you would too!
You press a button or a shortcut key to create a waypoint and write anything you want to describe it, then you see the marks on your map.
For instance, you click a button and it creates a waypoint of the X and Y coordinates from where you are and a window pops up for you write a description. You can mark mines, spots and player houses this way.
Also, you can have an option to show/hide the waypoints saved.
Since part of this system is already implemented in the game, I believe its easy to do.