The ornamental design for a modular towersegment, as shown and described.
FIG. 1 is an isometric view of a modular tower segment showing the new design with an example of its environment;
FIG. 2 is a view similar to FIG. 1, showing the modular tower segment alone;
FIG. 3 is a top end view thereof, the bottom end view being identical;
FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 2;
FIG. 5 is a right side view thereof, the left side view being identical; and,
FIG. 6 is a front side view thereof, the rear side view being identical.
The features on the modular tower segment that are shown in broken lines in FIG. 1 are for illustration purposes only and form no part of the claimed design.