The ornamental design for a memorialmarker, as shown and described.
FIG. 1 is a perspective view of my ornamental design for a memorial marker;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a front elevational view thereof, a rear being identical to the front; and,
FIG. 5 is a right side elevational view thereof; a left side being identical to the right side.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.