Code point
U+29EF
Glyph appearance depends on your fonts.
U+29EF
SmU+29EF ERROR-BARRED BLACK SQUARE is a Unicode 16.0.0 character in the Math Symbol category. It belongs to the Miscellaneous Mathematical Symbols-B block.
Choose the representation you need, then copy its value.
U+29EF
10735
⧯
⧯
E2 A7 AF
29EF
000029EF
%E2%A7%AF
\u29EF
\u29EF
\u29EF
\29EF