/sys$common/syshlp/helplib.hlb SET, PREFIX, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  $ SET VERIFY
  $ @TEST
  $ SET DEFAULT SYS$LOGIN
  $ SHOW DEFAULT
    USER$:[JENSEN]
  $ SET PREFIX "(!5%T) "
  $ @TEST
  (17:52) $ SET DEFAULT SYS$LOGIN
  (17:52) $ SHOW DEFAULT
    USER$:[JENSEN]

      This example demonstrates the difference between having and
      not having a prefix for verification. The first command turns
      on verification. (Verification must be turned on to see the
      prefix.) The second command invokes a test procedure to show
      what the output looks like without a prefix. The third and
      fourth lines reflect the contents of the test procedure invoked
      in the preceding command. The third command sets the prefix to
      an FAO control string so that the first five characters of the
      standard time will be shown for each command. The last command
      invokes the test procedure again to demonstrate what the output
      looks like with a prefix.