style a geojson point like a POI with leaflet/mapbox - leaflet

Question

I am using mapbox.js to render a mapbox map. I am trying to load geojson from my server that contain either a country polygon or a city coordinates (lon,lat).
I have been able to style the country polygons but not the city points/markers.
I am not able to modify the geojson to use mapbox simplestyle
Here is the code executed when the page loads (I changed the mapbox map ID):
var southWest = L.latLng(-90, -360), northEast = L.latLng(90, 360);
var bounds = L.latLngBounds(southWest, northEast);
var map = L.mapbox.map('map', 'MapboxMapID', { zoomControl: false, infoControl: true, detectRetina: true, maxBounds: bounds, minZoom: 2, legendControl: {position: 'topright'}});
new L.Control.Zoom({ position: 'bottomright' }).addTo(map);
map.fitBounds(bounds);
var locationsGroup = L.featureGroup().addTo(map);
and then when the user selects a country or city with a selectbox:
$("#select2-search-up").on("change", function (e) {
if (e.added) {
var location = L.mapbox.featureLayer().loadURL('/citiesCountriesID/' + e.added.id).on('ready', function(featLayer) {
this.eachLayer(function(polygon) {
polygon.setStyle({
stroke:false, fillColor:'red', fillOpacity:0.2
});
});
});
locationsGroup.addLayer(location);
} else {
locationsGroup.eachLayer(function (layer) {
if (layer._geojson[0]._id == e.removed.id) {
locationsGroup.removeLayer(layer);
}
});
}
});
Ideally I would like to display a different icon that the standard marker, but I could do with a small red square
Thank you for your inputs

Answer 1

In this example I did some circle markers but I'm pretty sure you can do other basic svg shps or your own .png pretty easy. http://bl.ocks.org/mpmckenna8/db2eef40314fe24e9177
This example from Mapbox also shows how to use a icon from their icon Library which has a lot of choices also. https://www.mapbox.com/mapbox.js/example/v1.0.0/l-mapbox-marker/
It might also help to see some of your geojson structure to see why it can't use simplestyle
In my bl.ocks example I loaded each of the geojson datasets separately
var begin = L.geoJson(start,{
pointToLayer:function(feature, latlng){
return L.circleMarker(latlng,{
radius:9,
fillColor: "orange",
fillOpacity:.7
})
}
})
Is how I set up my circles and I set a different L.geoJson to the other data which I left as the default markers.