Note, Danger
This is a warning icon, which is depicted in a yellow triangle with a bold black exclamation point. Emoji displayed on different platforms are somewhat different. Except for au by KDDI and Docomo platforms, which depict orange exclamation marks, other platforms display black exclamation marks. In addition, some platforms have a black, orange or red border around the triangle.
The emoji can be used not only to specifically warn or remind people of this behavior, but also to express serious, important and urgent matters, and sometimes it also means danger.
