Building Block

FIG. 1 is a front, left and bottom perspective view of a building block, showing our new design; FIG. 2 is a front view thereof; FIG. 3 is a rear view thereof; FIG. 4 is a left side view thereof; FIG. 5 is a right side view thereof; FIG. 6 is a top plan view thereof; FIG. 7 is a bottom plan view thereof; and FIG. 8 is a rear, right and bottom perspective view of the building block with an unclaimed lid shown in a state of use: FIG. 9 is another front, left and bottom perspective view of the building block with an unclaimed lid removed; and, FIG. 10 is a front, right and top perspective view thereof. The broken lines shown in the drawings illustrate portions of the building block that form no part of the claimed design.