VMS Help MACRO, /MIGRATION, Compiler Directives, .SYMBOL ALIGNMENT, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The .SYMBOL_ALIGNMENT directive is used to associate an alignment
    attribute with the fields in a structure when you know the base
    alignment. It is used in pairs. The first .SYMBOL_ALIGNMENT
    directive associates either longword (long) or quadword (quad)
    alignment with the symbol or symbols that follow. The second
    directive, .SYMBOL_ALIGNMENT none, turns it off.

    Any time a reference is made with a symbol with an alignment
    attribute, the base register of that reference, in effect,
    inherits the symbol's alignment. The compiler also resets the
    base register's alignment to longword for subsequent alignment
    tracking. This alignment guarantee enables the compiler to
    produce more efficient code sequences.