This technique is not commonly known to pen testers as it involves the hashing of an icon. This is actually another cool way of telling whether or not a server is running JBoss AS. We can MD5 hash the favicon.ico file (an icon file), as in the following screenshot:
Searching the hash in the OWASP favicon database will show us whether the server is running JBoss:
As the OWASP favicon database is very limited, we could always create our own database to carry out this activity.