Maps Marker Pro uses map icons from the Maps Icons Collection by Nicolas Mollet (http://mapicons.nicolasmollet.com/). By default, a preselection of about 100 icons (from more than 700 available icons) has been added to the plugin. On first activation of the plugin, the zip-file mapicons.zip gets unzipped into the directory \wp-content\uploads\leaflet-maps-marker-icons of your WordPress installation (note: you might have to enter your ftp-credentials once depending on your configuration) If you want to add more map icons, please download the desired icons from http://mapicons.nicolasmollet.com/ and upload them to the directory \wp-content\uploads\leaflet-maps-marker-icons