Under the Vienna Convention, a red-bordered triangle generally indicates a warning.
Warning signs alert road users to hazards or unusual conditions ahead, such as a junction, sharp bend, crossing, or steep descent. The triangle’s point may face upward or downward depending on the sign type and national system.
The Vienna Convention on Road Signs and Signals was concluded in 1968 to promote international consistency. It establishes broad sign categories and meanings, but countries retain some freedom over symbols, colors, dimensions, and supplementary plates.
The red border is therefore a strong international clue, not a guarantee that every country uses identical artwork. Regulatory signs, by contrast, commonly use circles, while information signs often use rectangular panels.