Code point
U+298B
Glyph appearance depends on your fonts.
U+298B
PsU+298B LEFT SQUARE BRACKET WITH UNDERBAR is a Unicode 16.0.0 character in the Open Punctuation category. It belongs to the Miscellaneous Mathematical Symbols-B block.
Choose the representation you need, then copy its value.
U+298B
10635
⦋
⦋
⦋
E2 A6 8B
298B
0000298B
%E2%A6%8B
\u298B
\u298B
\u298B
\298B