🔴 · Symbols › Shapes · Emoji 0.6 (2010)
🔴 is a solid red circle.
A red dot is a signal: live now, recording, a notification, an alert, or 'busy, don't disturb'. Next to 🟢 and 🟡 it works like a traffic light, and in emoji art it's a round red pixel.
Paint with 🔴 in the emoji art editor, or turn any photo into emojis with the image to emoji converter.
U+1F534🔴\1F534\u{1F534}\U0001F534%F0%9F%94%B4← 🈵 Japanese “no Vacancy” Button · 🟠 Orange Circle → · Symbol emoji library