Using the Warning Symbol
The warning sign is a triangle with an exclamation mark inside, the shape that road signs, machinery labels and safety standards use to mean "hazard ahead, read the details". The ISO 7010 general warning sign is exactly this: a black mark on a yellow triangle with a black border. Unicode added it as U+26A0 in 2003 in the Miscellaneous Symbols block, first as a plain text glyph, and it later gained an emoji presentation that reproduces the yellow-and-black look.
Plain triangle or yellow emoji
On its own ⚠ is drawn in the font colour, so it looks like a hollow outline in a paragraph and adapts to dark mode. Append the variation selector U+FE0F and it becomes ⚠️, the filled yellow triangle. Both are the same character, so a search matches either, but the emoji carries far more weight: in a message it reads as an alert, while the text form reads as a footnote marker. Software documentation and admonition boxes tend to use the text glyph; social posts nearly always use the emoji.
Spacing and placement
Put the sign at the start of the line it warns about, followed by a space and then the text: "⚠ Contains spoilers". Placing it at the end reads as an afterthought, and wrapping a sentence in two of them is common but noisy. In a list, one triangle per item is plenty. Do not combine it with ❗ in the same line; each is an attention marker and stacking them dilutes both.
Content warnings and moderation
Online communities have adopted ⚠️ as the standard prefix for content and trigger warnings, spoilers, flashing-image notices and "long thread" disclaimers. Moderators use it in pinned messages and rule lists, and support teams use it in status updates about outages. Because it has that established meaning, using it as pure decoration in a bio can make readers expect a caveat that never arrives; a decorative triangle from the aesthetic symbols page does the same visual job without the implied alert. Some automated filters treat a burst of ⚠️ in a username or spam message as a signal, so keep it to one.
Rendering
Every phone and desktop font from the last fifteen years includes the text glyph, and every emoji font includes the yellow version. The older caution sign ☡ at U+2621 is a different character with almost no font support, so it usually appears as a box; avoid it. Stronger marks exist for stronger meanings: ⛔ for forbidden, 🛑 for stop, ⚡ for electrical hazards and the skull symbol ☠ for poison or danger to life.
Pairing the plain triangle with the heavy letters from the bold fonts generator gives a caution-tape header for a Discord channel or a stream schedule, and the text form survives in game chats and profiles that strip emoji.