VMS Help SET, PROMPT, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 string

    Specifies the new prompt string. The following rules apply:

    o  All valid ASCII characters can be used.

    o  No more than 32 characters are allowed.

    o  To include spaces or lowercase letters, enclose the string
       in quotation marks (" ").  Otherwise, letters are converted
       automatically to uppercase; leading and trailing spaces are
       removed.

    If you do not specify the string parameter with the SET PROMPT
    command, the default DCL prompt ($  ) is restored.