We claim the ornamental design for a toilet seat cover, as shown and described.
FIG. 1 is a front elevational view of a toilet seat cover of our new design, the rear elevational view, left-side elevational view, and right-side elevational view all being identical;
FIG. 2 is a perspective view thereof; and,
FIG. 3 is a top plan view of FIG. 2, the bottom plan view being a mirror image thereof.
The broken lines showing a toilet in FIG. 1 depict environmental matter and form no part of the claimed design. It is understood that the front, left, right and rear elevational views of all embodiments are identical.