This usually happens if you’re using a CDN or set your media on a different domain/hosting. So if your icons are showing like this, it may be because of a CORS-related issue, here’s how to fix it:

Apache {#apache} Look for the#

.htaccess file at the root of your WordPress installation and add the following to it:

<FilesMatch "\.(ttf|otf|woff)$">
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin "*"
</IfModule>
</FilesMatch>

IIS7 {#iis} Look for the#

web.config file at the root of your WordPress installation and merge it with the following:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
 <system.webServer>
   <httpProtocol>
     <customHeaders>
       <add name="Access-Control-Allow-Origin" value="*" />
     </customHeaders>
   </httpProtocol>
 </system.webServer>
</configuration>

http://en.wikipedia.org/wiki/Cross-origin_resource_sharing

Nginx {#nginx} configuration#

The following Nginx configuration enables CORS, with support for preflight requests.

#
# Wide-open CORS config for nginx
#
location / {
     if ($request_method = 'OPTIONS') {
        add_header 'Access-Control-Allow-Origin' '*';
        #
        # Om nom nom cookies
        #
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        #
        # Custom headers and headers various browsers *should* be OK with but aren't
        #
        add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
        #
        # Tell client that this pre-flight info is valid for 20 days
        #
        add_header 'Access-Control-Max-Age' 1728000;
        add_header 'Content-Type' 'text/plain charset=UTF-8';
        add_header 'Content-Length' 0;
        return 204;
     }
     if ($request_method = 'POST') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
     }
     if ($request_method = 'GET') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
     }
}

http://enable-cors.org/server_nginx.html

Icons not appearing after site migration#

Please see this article After site migration, icons are looking strange or not appearing at all