What each angle symbol means
∠ is the standard angle sign. ∠ABC names the angle at point B, the middle letter, formed by the rays BA and BC. US textbooks write m∠ABC for the measure of that angle, while some books use ∡ (measured angle) for the size instead.
∢ marks a spherical angle, used in spherical geometry. ∟ and ⊾ stand for a right angle (exactly 90°), just like the small square drawn in the corner of a diagram, and ⊿ is a right triangle. The variants in the second grid, such as ⦟ (acute angle), are rarer and mostly appear in specialist texts.
Writing angle sizes
Angles are usually measured in degrees with the degree symbol °. For finer detail, a degree splits into 60 minutes, written with the prime ′, and a minute into 60 seconds, written with the double prime ″. Map coordinates use this format, for example 40° 26′ 46″ N.
Primes are not the same as the straight apostrophe and quote mark on your keyboard, although those are common stand-ins. In math and physics, angles are often given in radians instead: 90° = π/2 rad, which is why the pi symbol shows up so often in trigonometry.
How to type the angle symbol
There is no Alt code or Mac Option shortcut for ∠. In Microsoft Word, type 2220 and press Alt + X. On a Mac, open the Character Viewer (Control + Command + Space) and search for "angle". In HTML, use ∠.
In LaTeX, write \angle for ∠; the amssymb package adds \measuredangle for ∡ and \sphericalangle for ∢. For the degree sign, press Option + Shift + 8 on a Mac or Alt + 0176 on Windows. Do not confuse the angle sign with angle brackets ⟨ ⟩, which are on the bracket symbols page.