The ornamental design for a coverplate for switches, as shown and described.
FIG. 1 is a front perspective view of a cover plate for switches;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a right side perspective view thereof;
FIG. 4 is a top perspective view thereof;
FIG. 5 is rear elevation view thereof; and,
FIG. 6 is a side view thereof, the opposite side being a mirror image.
The broken lines shown in the figures are for the purpose of illustrating portions of the cover plate for switches that form no part of the claimed design.