aestheticsymbols
Use in a combo

Left corner bracket copy & paste

「 is left corner bracket, a plain-text Unicode symbol from the CJK Symbols and Punctuation block. On Aesthetic Symbols it lives in the borders & shapes collection. As plain text it takes on the font and colour of wherever you paste it — a bio, a username, a caption or a stream title.

Unicode
U+300C
HTML entity
「
CSS content
\300C
JavaScript
\u{300C}
UTF-8 bytes
E3 80 8C
Made of

U+300C 「 · CJK Symbols and Punctuation

Will it show up? · Long-established text symbols

Plain-text characters from blocks that mainstream desktop and mobile fonts have covered for years. These are the safe ones.

Worked out from how each character is encoded, not from a test on a real device.