I'm assuming that whatever mail server the
firstname.lastname@example.org account uses subaddressing of the sort that guarantees mail sent to
email@example.com gets to the
team mailbox. If a SE employee could confirm one way or the other, I'd appreciate it. The rest of this question depends on that assumption.
Each SE site's Community user has
firstname.lastname@example.org listed as its e-mail address, so has the default pale-blue gravatar associated with that address. Individual sites may wish to personalize their Community user's gravatar. This is possible if (a) the e-mail address used is particular to that site, which is possible by means of subaddressing as
email@example.com or whatever, and (b) the site mods are granted access to
gravatar.com's account for that subaddress. (How each site's mods decide on an gravatar can be decided by them locally.)
That's my proposal.
I recognize that choosing an avatar for Community is very low priority; on the other hand, it's fairly easy.
(I see that this was proposed in comments to
http://meta.stackexchange.com/q/119560 but never in a question.)