Mumble provides a native "Overlay" that allows you to see who is talking, while in-game. You can choose the font, location on the screen, size, colors, and even custom textures for each user.
To create a custom user texture, just create a 600x60 image (we recommend a 24-bit PNG with transparency) and go to Server -> Change Texture in the Mumble client. You can set that image to your texture, and other people will see it when you talk, rather than your name.
Mumble allows you a wide rage of control over the overlay, including exact positioning, deciding what you want to show (show everyone, show only people who are talking, etc), colors, direction that the list grows in, etc.
From the official Mumble wiki:
Games with Major Issues
Games that are known to have minor issues with the Mumble overlay:
If you would like to disable the overlay for a certain game (because you do not want it in that particular game, or that game has issues with the overlay), and do not want to disable the overlay altogether, put a file named
nooverlay (without any extensions) in the same folder as the game executable is located. This will tell Mumble that you do not want the overlay in this particular game.