The ornamental design for a lockboxbumper, as shown and described.
FIG. 1 is a top, rear perspective view of a lock box bumper showing our new
design;
FIG. 2 is a top, front perspective view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a reduced perspective view thereof, the knob, a portion of a
door, and the lock box being shown on broken lines for illustrative
purposes only.