VMS Help DCL Tips, Symbol  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    A symbol is an entity that has a name and a value. The name can
    consist of letters, digits, underscores (_) and dollar sign
    ($). It can be composed of up to 255 characters. The value of
    the symbol can be a 32-bit integer or a string with zero to 255
    characters.

    Symbols are defined in DCL with the assignment statement. This is
    described under the Help topic SYMBOL_ASSIGN.