FIG. 1 is a top side perspective view showing my new design for a line marker overcover, the broken lines are shown for illustrative purposes only and form no part of the claimed design;

FIG. 2 is a bottom side perspective view thereof, the broken lines are shown for illustrative purposes only and form no part of the claimed design;

FIG. 3 is a side elevational view thereof, the broken lines are shown for illustrative purposes only and form no part of the claimed design;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a side elevational view thereof showing typical positioning on an existing marker, the broken lines are shown for illustrative purposes only and form no part of the claimed design.