We claim the ornamental design for an asset tracker, as shown and described.
FIG. 1 is a top-front perspective view of an asset tracker, showing our new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a top-rear perspective view of thereof.
The dot dash lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are included for the purpose of illustrating portions of the asset tracker the broken lines form no part of the claimed design.