The ornamental design for a clamp, as shown and described.
FIG. 1 is a top plan view of the clamp showing my new design;
FIG. 2 is a side elevational view thereof;
FIG. 3 is a same side elevational view thereof, showing the clamp in the
open position with the paper sheets being shown in broken lines for
illustrative purposes only;
FIG. 4 is an exploded view thereof with the components of the clamp being
shown separated for purposes of disclosure only.