Reversed Not Sign

It is the mirrored counterpart of ¬ and a line-start marker.

In standard mathematical logic, ¬ (with the vertical hook on the right) means "not." ⌐ flips that shape so the vertical hook sits on the left and the horizontal bar reaches to the right. In the ISO technical symbol sets and HTML/MathML, it carries the entity name bnot ("backwards not") for specialized mathematical and logical notation that calls for a left-handed or paired negation mark.

In computing, Unicode also records the alias "beginning of line" for ⌐. Just as ¬ has sometimes been used in editors and technical manuals to show where a line wraps or ends, ⌐ provides the matching left-facing corner to mark where a line starts. It was included in the original IBM PC character set (Code Page 437 at position 169) alongside ¬ (at position 170) so technical printers and terminals had both left and right hooks.

Why do people use ⌐ in messages and text art?

Its high corner shape makes a ready-made earpiece or gun barrel.

Because ⌐ sits near the top of the line with a crisp left hook, internet text artists adopted it long ago. Its most famous role is the temple of a pair of sunglasses in the "deal with it" kaomoji (⌐■_■), often preceded by ( •_•)>⌐■-■ to show someone putting the shades on.

You will also spot it in box-like borders, retro MS-DOS art, or flipped-table faces where a sharp upper-left angle is needed and a full box-drawing character like ┌ would drop too low.