Like when you see people post things, and you see their picture, and under that it says contributor, like literally under that. That's the only way I can describe it, for example: I am a AD/ DL. But on some other people's it says TD or IS
If you go to your profile, under the about me section, click on the little pencil next to "AB/DL Identity" and it will list all the things you can choose from.
**** EDIT - I clicked them all and did not see TD or IS, so I have no idea what they stand for?