In playing cards, the diamond suit typically symbolizes wealth or the merchant class. Therefore, it's sometimes used in conversations about money and luxury goods, or to indicate a high rank in games.

In K-pop fandoms, it's sometimes used as an icon to symbolize a specific group, and it's very familiar in video games as a symbol for high ranks, like 'Diamond tier.' So for teens and people in their 20s, it's often used to signify skill or value.