You can place markers in the /img/markers folders, and then select them on the settings page. This should work if you keep the same format.
If you use a different format, you should open the /js/wpsl-gmap.js search for ‘function addMarker’ and change the numbers in the code below to the new format.
mapIcon = {
url: markerPath,
scaledSize: new google.maps.Size( 24,35 ), //retina is 50% of the real format
origin: new google.maps.Point( 0,0 ),
anchor: new google.maps.Point( 12,35 )
};
Thanks for the reply Tijmen, I will try them out!