Stackable building block

Description

FIG. 1 depicts a three-quarters perspective view of a new and ornamental design for a stackable building block.

FIG. 2 depicts a front elevational view thereof of a new and ornamental design for a stackable building block.

FIG. 3 depicts a rear elevational view thereof of a new and ornamental design for a stackable building block.

FIG. 4 depicts a left side elevational view thereof of a new and ornamental design for a stackable building block.

FIG. 5 depicts a right-side elevational view thereof of a new and ornamental design for a stackable building block.

FIG. 6 depicts a top plan view thereof of a new and ornamental design for a stackable building block; and,

FIG. 7 depicts a bottom plan view thereof of a new and ornamental design for a stackable building block.

The broken lines in the portions of the article shown form no part of the claimed design.

Claims

I claim the ornamental design for a stackable building block, as shown and described.