"Red triangle" typically refers to a warning symbol or sign used to indicate caution or danger. It can be seen in road signs or other contexts where there is a need to alert people about potential risks or hazards. Full definition
It starts off with a plain upside - down red triangle with a C on it. (metacritic.com)
Be sure to read the comments within the file (marked with a little red triangle on some of the cells) if you have questions. (vertex42.com)
I was experimenting with panels, and I did a three part painting that was a large green rectangle, a large yellow rectangle with a large red triangle. (ronnielandfield.com)