sb_sortsources
Ordering instructions for server browser sources list are stored in this variable. You can order source server in Server browser by pressing Ctrl+1, Ctrl+2 and Ctrl+3. Sequence of your desired combination will be stored in this variable, newest keys first.
E.g.: 3-21 means you've pressed Ctrl+1, Ctrl+2, Ctrl+2 and Ctrl+3 so your sources are now ordered by server count, last update time and source name.