set status_user [<text>]
This variable is user-definable. The text that is assigned to it is displayed in the status bar as %U (or %0, see below). The expando is treated literally inside STATUS_USER, and has no special meaning. This variable is provided so the user can make arbitrary information available in the status bar.
Setting some custom string for the status bar:
/set status_user Client configured by IRC Systems, Inc.
There are actually 9 additional user-definable variables, STATUS_USER1 through STATUS_USER9. Each has a unique expando, %1 to %9.