Image from Tom Van Flandern's web site metaresearch.org
North is up in this picture, so the face and hence the "sun calendar"
are orientated anticlockwise about 20 degrees, which means the "sundial"
would work. At a Martian equinox the pointer would fall around the center,
then for half the year as the North experienced summer, the shadow would
move up the scale and then down to the equinox again.
Evidence the center of the "sun calendar" is elevated can be seen below.
Copyright © 1998 by Malin Space Science Systems, Inc.
This dark area appears to have some pointer like shape there, but pointing away from the marks. When the shadow is on the other side (in the afternoon) it must point towards the marks.