Is this something hidden that google shares with its internal systems (gmail uses android icons as well) or is it just data that’s sent inside the normal Jabber traffic, that other clients ignore?
Edit:
I’m referring to “How does android/gmail know when to associate these icons:”

Instead of the default:

The XMPP specification defines a resource identifier that clients can use to identify themselves. Clients connecting via Android usually have a resource identifier, that begins with
ANDROID, so it’s easy to identify connected Android clients.It depends on your client if you are able to see the resource identifier itself. For example I’m using Trillian to connect to Google Talk and other XMPP systems, and that one shows the client’s resource identifier in the contact list. In case multiple clients are connected to the same account, this also allows you to see which clients are connected (as each used identifier is shown).