Node marks are colored concentric circles, boxes, or hexagons around nodes.
They are created by:
m -t time -n mark name -s node -c color -h shape -o color
and can be deleted by:
m -t time -n mark name -s node -X
Note that once created, a node mark cannot change its shape. The possible
choices for shapes are, circle, box, and hexagon. They are defined as
lowercase strings exactly as above. A nam trace showing a node mark is:
m -t 4 -s 0 -n m1 -c blue -h circleindicating node 0 is marked with a blue circle at time 4.0. The name of the mark is m1.