Non-Exclusive Markers

Show and hide different categories of markers
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Non-Exclusive Markers</title>
  <meta name='viewport' content='width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no' />
  <script src='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.js'></script>
  <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.css' rel='stylesheet' />
  <!--[if lte IE 8]>
    <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.ie.css' rel='stylesheet'>
  <![endif]-->
  <style>
    body { margin:0; padding:0; }
    #map { position:absolute; top:0; bottom:0; width:100%; }
  </style>
</head>
<body>
<style>
#filters {
    position: absolute;
    top: 75px;
    left: 10px;
    z-index: 100;
    padding: 5px;
    background: #fff;
}

#filters ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
}
</style>
<div id='map-ui'>
    <form id='filters'>
        <ul id='options'>
            <li><input type='checkbox' checked=checked class='filter'
                       name='filter' id='fast-food' value='fast-food'/><label for='fast-food'>fast-food</label></li>
            <li><input type='checkbox' checked=checked class='filter'
                       name='filter' id='bicycle' value='bicycle'/><label for='bicycle'>bicycle</label></li>
            <li><input type='checkbox' checked=checked class='filter'
                       name='filter' id='bar' value='bar'/><label for='bar'>bar</label></li>
        </ul>
    </form>
</div>
<div id='map'></div>
<script>
var map = L.mapbox.map('map', 'examples.map-zr0njcqy');
var filters = document.getElementById('filters');
var checkboxes = document.getElementsByClassName('filter');

function change() {
    // Find all checkboxes that are checked and build a list of their values
    var on = [];
    for (var i = 0; i < checkboxes.length; i++) {
        if (checkboxes[i].checked) on.push(checkboxes[i].value);
    }
    // The filter function takes a GeoJSON feature object
    // and returns true to show it or false to hide it.
    map.markerLayer.setFilter(function (f) {
        // check each marker's symbol to see if its value is in the list
        // of symbols that should be on, stored in the 'on' array
        return on.indexOf(f.properties['marker-symbol']) !== -1;
    });
    return false;
}

// When the form is touched, re-filter markers
filters.onchange = change;
// Initially filter the markers
change();
</script>
The code and documentation to mapbox.js is hosted on GitHub where you can contribute changes and improvements.