"to identify which firewall I am working on."
So you don't know what firewall is what based upon name, fqdn, IP?
Couldn't you just use names like pf-sitename.domain.tld or pfsense.sitename.domain.tld, pfsense.sitedomain.tld, pfsense.othersitedomain.tld, etc.. or if just using IP would they be different IP?
I like to apply different themes to the 3 pfsense boxes that I administer. Have you ever tried to compare 3 sets of ipsec settings across 3 different firewalls? It can get very confusing, and having a strong visual reference helps keep my head on straight.
Sure, the address in the URL bar is a logical equivalent, but a different theme and image is more reliable when dealing with humans.