FIG. 1 is a perspective view of a seal strip for window shades. FIG. 2 is a left side thereof. FIG. 3 is a right side thereof. FIG. 4 is a top plan view thereof. FIG. 5 is a bottom plan view thereof. FIG. 6 is a front elevation view thereof; and, FIG. 7 is a rear elevation view thereof. The broken lines are for illustrative purposes only and form no part of the claimed design.