Squared Three

It is the third-base marker from Japanese baseball broadcasts. Baseball is one of Japan’s most popular sports, and broadcasts routinely show which bases have runners on them. In Japanese the bases are counted with plain numerals: 一塁, 二塁, 三塁 (ichirui, nirui, sanrui: first, second, third base). Japanese broadcast text systems carried a small set of boxed characters for exactly this job: 🈩 (一) for first base, 🈔 (二) for second and 🈪 (三) for third. Unicode added a large batch of these Japanese TV symbols in 2009, which is why 🈪 sits beside signs like 🈚 (free of charge), 🈯 (reserved) and 🈲 (prohibited).

Away from a scoreboard it simply reads as “three in a box”. Anyone who reads Japanese or Chinese sees the numeral 三; a square around a character often works as a label or an abbreviation, the way a boxed “3” would in a diagram. It isn’t a symbol for expressing a feeling. If it turns up in a message, it is most likely a decorative three, a find from a symbol picker, or text pasted from Japanese sports coverage.

Why does it look so plain, or like an empty box?

Because it is a text character, not an emoji. Several neighbours from the same TV set did get emoji status and bright colour art (🈚 🈯 🈲 🈴 🈵), but the three base markers were left as ordinary text. Your font decides what 🈪 looks like: a thin square with 三 inside on many phones and modern computers, a blank rectangle or a question mark where the font or older software lacks it. The character itself hasn’t changed. For that reason it is a risky choice for anything that must be readable everywhere, such as a username or a headline.