The ornamental design for a rooftop vent clasp, as shown and described.
FIG. 1 is a front, left side perspective view of the rooftop vent clasp in the engaged state in an embodiment of the present invention;
FIG. 2 is a front, left side perspective view thereof in the disengaged state;
FIG. 3 is a front left side perspective view thereof in the engaged state as attached to the vent hood;
FIG. 4 is a front left side perspective view thereof in the disengaged state as attached to the vent hood;
FIG. 5 is a left side elevation view thereof in the engaged state;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a front elevation view thereof; and,
FIG. 9 is a rear elevation view thereof.
The broken line showing of the vent hood and vent is included for the purpose of illustrating use and environment and forms no part of the claimed design.