What ⦞ means
It is a plural angle sign in one documented proposal. MathML, a format for mathematical notation, classifies it as an infix operator—a sign between parts of an expression—but gives no universal definition.
In 2007, a Unicode proposal cited the 14th-edition Chicago Manual of Style, an editors’ guide, and a Persian/Arabic book-preparation guide by Mir Šamseddin Adib-Soltani. It noted references in other languages even though s marks an English plural, but said use in mathematical publications was not clearly attested.
Don't confuse it with
1Questions people ask
2Can a font make ⦞ disappear?
Yes. If the chosen font lacks this rare math glyph, it may be missing or look different. Check it in a math-capable font.
How can I type ⦞?
It has no standard key; search your document editor’s character list for “angle with s inside.”
How to type ⦞
⦞\299ECodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.