aestheticsymbols
Use in a combo

Comet (text style) copy & paste

☄︎ is comet (text style), a plain-text Unicode symbol built from several characters from the Miscellaneous Symbols block. On Aesthetic Symbols it lives in the stars & celestial collection, tagged star. 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+2604 U+FE0E
HTML entity
☄︎
CSS content
\2604 \FE0E
JavaScript
\u{2604}\u{FE0E}
UTF-8 bytes
E2 98 84 EF B8 8E
Made of

U+2604 ☄ · Miscellaneous Symbols

U+FE0E text-style selector · Variation Selectors

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.