Usage: SET INPUT_PROMPT <input prompt string>
  Allows you to change the prompt that will be displayed in the
  input line before any text you type.  Normally, there is no
  prompt, but you can specify any string.  To turn off a prompt,
  use /set -INPUT_PROMPT. Using the special variable $T is
  useful as in INPUT_PROMPT as it shows what the current 
  destination is for any input, such as a channelname or nickname
  if you are using query.