Custom markers with text

<!DOCTYPE html>
<html>
<head>
  <script src='https://api.tiles.mapbox.com/mapbox.js/v0.6.6/mapbox.js'></script>
  <link href='https://api.tiles.mapbox.com/mapbox.js/v0.6.6/mapbox.css' rel='stylesheet' />
  <style>
    body { margin:0; padding:0; }
    #map { position:absolute; top:0; bottom:0; width:100%; }
  </style>
</head>
<body>
<style>
.marker-image {
    width:50px;
    height:50px;
    border:1px solid #000;
    background:#eee;
    margin-left:-26px;
    margin-top:-26px;
    pointer-events:all;
    position:absolute;
    text-align:center;
    line-height:50px;
}
</style>
<div id='map'></div>
<script>
    // Create map
    var map = mapbox.map('map');
    map.addLayer(mapbox.layer().id('examples.map-vyofok3q'));

// Create and add marker layer
    var markerLayer = mapbox.markers.layer().features([{
        "geometry": { "type": "Point", "coordinates": [-74.00, 40]},
        "properties": { "number": 2 }
    }, {
        "geometry": { "type": "Point", "coordinates": [-75.00, 40]},
        "properties": { "number": 4 }
    }]).factory(function(f) {
        var div = document.createElement('div');
        div.className = 'marker-image';
        div.innerHTML = f.properties.number;
        return div;
    });

map.addLayer(markerLayer)
        .setExtent(markerLayer.extent());

// Attribute map
    map.ui.attribution.add()
        .content('<a href="https://mapbox.com/about/maps">Terms &amp; Feedback</a>');
</script>
</body>
</html>

Modified http://api.tiles.mapbox.com/mapbox.js/v0.6.6/mapbox.js to a secure url

https://api.tiles.mapbox.com/mapbox.js/v0.6.6/mapbox.js