The ornamental design for message sign board, as shown and described.
FIG. 1 is a front elevational view of a message sign board showing our new
design, with the broken line showing for illustrative purposes only and
forming no part of the claimed design, with the rear being flat and
unornamented;
FIG. 2 is a right side elevational view thereof, with the opposite side
being a mirror image;
FIG. 3 is a front elevational view of a second embodiment thereof, with the
broken line showing for illustrative purposes only and forming no part of
the claimed design, and with the rear being flat and unornamented; and,
FIG. 4 is a right side elevational view thereof, with the opposite side
being a mirror image.