Some traffic signs are in the shape of a what instead of a circle?

Answer: A — Arrow

Arrows are used on some signs because their shape instantly communicates direction and movement. The arrow design quickly tells you which way you must go or which lane is designated, without needing to read words. This makes directional instructions easy to recognize at a glance, which is why you’ll see arrow-shaped signs for things like one-way streets and lane restrictions. Circular signs stay for other kinds of information, but the arrow shape specifically signals direction.