A triangular red flag on a post. Often seen in golf clubs, as shown in the ⛳ flag in hole emoji. Mostly used to emphasize the importance or the urgency of something.
In dating red flag symbol is used as a caution, or as warning signal or sign about worrisome behavior from a prospective date.
In October 2021 Twitter was blowed with a viral trend where people using the red flag emoji to signal opinions and behaviors that they find to be problematic: “going all day without talking to me 🚩🚩🚩”
When a lot of the tweets are serious, many of them are jokes: “doesn't think of me when he looks at the moon 🚩”