What ∺ means
∷ has a documented use as a proportion sign. William Oughtred used it in the proportion a.b::c.d in his mathematics book Clavis Mathematicae, composed about 1628 and published in 1631. These dates document ∷, not the origin of ∺.
Don't confuse it with
1Questions people ask
1Why does ∺ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ∺
Windows (Word)
Alt+XType 223A, then Alt+X to get ∺.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “geometric proportion”.
Linux
Ctrl+Shift+UType 223a, then Enter or Space.
HTML
∺CSS
\223AWord for Windows
To type ∺ in Word for Windows, enter `223A` and press `Alt+X`.
HTML
Use the named character reference `∺`.
Codes and encoding1 code points
HTML decimal
∺
HTML hex
∺
CSS content
content: "\223A";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%88%BA
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.