The ornamental design for a blind for carts, as shown.
FIG. 1 is a front perspective view of a blind for carts showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right side elevational view thereof, the left side being a mirror image thereof; and,
FIG. 5 is a top plan view thereof.
The broken line showing the cart in FIGS. 1-5 illustrates the environment in which the design is used, assists in showing how the claimed design appears when used, and forms no part of the claim.