Forget about a font and use a background image!
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" >
<head>
<title>Select :after pseudo class/element</title>
<style type="text/css">
.close {
background:url(http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/images/ui-icons_222222_256x240.png) NO-REPEAT -96px -128px;
text-indent:-10000px;
width:20px;
height:20px;
}
</style>
</head>
<body>
<input type="button" class="close" value="Close" />
<button class="close">Close</button>
</body>
</html>
This will be more accessible for users visiting the page with a screen reader.