You could use the iconify search command.
So if you extract the severity level out into a field named "severity", you could do something like :
yourinitialsearch | iconify severity
http://docs.splunk.com/Documentation/Splunk/latest/SearchReference/Iconify
Hello,
have a look here, but it will requires some web development knowledge, but it works:
http://docs.splunk.com/Documentation/Splunk/latest/Developer/UseCSS