Lift Arm

FIG. 1 is a perspective view of an ornamental design for a lift arm, which shows our new design; FIG. 2 is a front elevational view of the lift arm of FIG. 1 ; FIG. 3 is a rear elevational view of the lift arm of FIG. 1 ; FIG. 4 is a left side elevational view of the lift arm of FIG. 1 ; FIG. 5 is a right side elevational view of the lift arm of FIG. 1 ; FIG. 6 is a top plan view of the lift arm of FIG. 1 ; FIG. 7 is an enlarged top plan view of the lift arm from line 7 of FIG. 6 ; and, FIG. 8 is a bottom plan view of the lift arm of FIG. 1 . The broken lines in the drawings illustrate portions of the lift arm that form no part of the claimed design. The dot dash dot lines in FIGS. 6 and 7 are notating enlarged views and form no part of the claimed design.