We claim the ornamental design for an hammer, as shown and as described.
FIG. 1 is a perspective front view of the hammer showing one face of the hammer.
FIG. 2 is a perspective back view of the hammer showing another face of the hammer.
FIG. 3 is a side view of the hammer.
FIG. 4 is the other side view of the hammer.
FIG. 5 is the front view of the hammer showing one face of the hammer.
FIG. 6 is a back view of the hammer showing another face of the hammer.
FIG. 7 is a top view of the hammer.
FIG. 8 is bottom view of the hammer; and,
FIG. 9 is a perspective front view of the hammer showing a nail attached to the magnetic face of the hammer.
The broken line showing of the nail is provided for purposes of environment and forms no part of the claimed design. The Handle of the hammer and the screw heads are shown in broken line since they form no part of the claimed design.