Usage: ON [#|+|-|^|&|@]OS_SIGNAL [-|^]<parameters> [action]
  This is activated whenever a signal is received.
  The parameters for the action are as follows:
    $0    the signal that occured, such as "INFO" or "USR2"
  There are some limitations with OS_SIGNAL support and
  /WINDOW CREATE.
  Signals received by sub windows are not shown.