Tracy,
  A couple of quick notes.  First, I believe that TELL and WARN disallow *all*
escape sequences *except* those which affect the text attributs (ESC &d...).
Also, the problem is somewhat more serious than just playing tricks on newbies.
With the right escape sequences, one can execute commands on the victim's
terminal and remove the evidence . . . commands such as

  :ALTUSER ME.OVERHERE;CAP=+SM

Ted
--
Ted Ashton ([log in to unmask]), Info Sys, Southern Adventist University
          ==========================================================
The art of discovering the causes of phenomena, or true hypothesis, is like
the art of decyphering, in which an ingenious conjecture greatly shortens
the road.
                        -- Leibniz, Gottfried Whilhem (1646-1716)
          ==========================================================
         Deep thoughts to be found at http://www.southern.edu/~ashted