The following image shows my most requested, simple-style map key:
Default placement is shown here:
We can write whatever you need and the colors of the map key will match the colors in map.
Or, if you are looking for something a little more special, there are monograms, compass roses and more elaborate map keys available.
Again, we can write whatever is needed.
A closer look to compass roses for world maps: (click to enlarge)
Map key badges:
And this is how we can place these items in the world map: