In Precise (12.04), when I login to lightdm, using the unity-greeter, there's a white circle by my name. For the standard DEs like Unity or XFCE, the circle has a representative icon (Ubuntu symbol or little mouse resp.). I have a session for Awesome window manager which was added when I installed Awesome, but it just shows a blank white circle. I'd like to know how to add an icon to it, or at least some indicator, as unity-greeter doesn't show you what session is set until you click on the circle.
I found another question about changing the session names. The answer for it said to change the names in the desktop files in
/usr/share/xsessions. Unfortunately, while there is an icon field in those desktop files, they are all blank (Caveat: I no longer have Unity installed, so maybe the Unity one would not be blank. But the Xubuntu desktop file has it blank even though the icon shows in unity-greeter).
Update: Here's the png I use as a badge for Awesome. It's not great, but looks reasonably nice: