aestheticsymbols
Use in a combo

Ballot X copy & paste

✗ is ballot x, a plain-text Unicode symbol from the Dingbats block. On Aesthetic Symbols it lives in the charms & marks collection, tagged cross. 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+2717
HTML entity
✗
CSS content
\2717
JavaScript
\u{2717}
UTF-8 bytes
E2 9C 97
Made of

U+2717 ✗ · Dingbats

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.