If Command Extensions are enabled the PROMPT command supports the following additional formatting characters: $+ zero or ...

If Command Extensions are enabled the PROMPT command supports
the following additional formatting characters:

  $+   zero or more plus sign (+) characters depending upon the
       depth of the PUSHD directory stack, one character for each
       level pushed.

  $M   Displays the remote name associated with the current drive
       letter or the empty string if current drive is not a network
       drive.