I claim the ornamental design for a top cover for a drinking vessel, as shown and described.
FIG. 1 is a bottom perspective view of a top cover for a drinking vessel according to a first embodiment of the new design;
FIG. 2 is a top view of the first embodiment;
FIG. 3 is a bottom view of the first embodiment;
FIG. 4 is a front elevation view of the first embodiment, the rear elevation view (not shown) being substantially similar to the front elevation view; and,
FIG. 5 is a right side elevation view of the first embodiment, the left side elevation view (not shown) being substantially similar to the right side elevation view.
The broken lines in FIGS. 1 and 3 are included for the purpose of illustrating a portion of the interior that forms no part of the claimed design.