It seems to me as if the icon which appears next to my name in the forums is a miniaturization of the logo for the last team that I signed into. I would like to upload a picture for the forums that does not change every time. I think that adding a field to the "My Account" tab would be a simple way to do this, unless I am all wet, again.

I believe the avatar shown is your team in league's forums you are on. This extends to the global forums too.

In other words, it uses your team logo for whatever league you are currently signed in to. I love this because it also shows everyone else's logo for that league. So, I'd rather that not change.