Due to some servers configurations, icons font can’t be loaded properly, as a result your icons don’t show in your site. To solve this issue, go to your hosting/server admin page, find .htaccess file in your installation folder, open it and paste this code:

<FilesMatch "\.(eot|font.css|otf|ttc|ttf|woff)$">
Header set Access-Control-Allow-Origin "*"

Save the file, now your icons should be visible.