I don't know why, but my glyphicons from Bootstrap (3.3.7) are missing, they are being substituted by a normal and ugly square. Here is an example of code that calls a missing glyphicon:
        <button type="button" class="btn btn-default">
          <span class="glyphicon glyphicon-star" aria-hidden="true"></span> Star
        </button>
And here it is the Bootstrap part that contains glyphicon's font:
 @font-face {
  font-family: 'Glyphicons Halflings';
  src: url('../fonts/glyphicons-halflings-regular.eot');
  src: url('../fonts/glyphicons-halflings-regular.eot?#iefix') format('embedded-opentype'), url('../fonts/glyphicons-halflings-regular.woff2') format('woff2'), url('../fonts/glyphicons-halflings-regular.woff') format('woff'), url('../fonts/glyphicons-halflings-regular.ttf') format('truetype'), url('../fonts/glyphicons-halflings-regular.svg#glyphicons_halflingsregular') format('svg');
}