What does Black Square Button look like on HTC?

On HTC it is the design shipped in Sense 8, shown above at full size. Older revisions are listed beneath it.

When did HTC add Black Square Button?

HTC first drew Black Square Button in Sense 7, released March 30, 2015.

HTC Corporation has shipped 2 versions of Black Square Button. Each is dated, so you can see when the design changed.

HTC

HTC Corporation has drawn Black Square Button 2 times. Every revision HTC has shipped is below, newest first.

What does Black Square Button look like on HTC?: On HTC it is the design shipped in Sense 8, shown above at full size. Older revisions are listed beneath it.
When did HTC add Black Square Button?: HTC first drew Black Square Button in Sense 7, released March 30, 2015.
How many times has HTC redrawn Black Square Button?: HTC Corporation has shipped 2 versions of Black Square Button. Each is dated, so you can see when the design changed.

HTC artwork for this emoji spans 2015 to 2016.