The ornamental design for a hammer, as shown and described.
FIG. 1 is a perspective view of a hammer, showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right elevation side view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is an enlarged right side elevation view thereof taken along indication area 9 of FIG. 6;
FIG. 10 is a cross-sectional side view along the line 10-10 in FIG. 9;
FIG. 11 is a cross-sectional side view along the line 11-11 in FIG. 9; and,
FIG. 12 is a cross-sectional side view along the line 12-12 in FIG. 9.
The dashed lines depict portion of the article that form no part of the claimed design. The dash-dot-dot lines depict boundaries between the claimed part and non-claimed part and form no part of the claimed design. The dash-dot lines in the drawings depict the border of the enlarged portion that forms no part of the claimed design.