What ㎆ means
It means megabyte, written as MB. The square let Latin letters occupy one East Asian character cell in mixed-width text. Unicode links square Latin abbreviations mainly to Korean standards, and square Japanese katakana (a syllabic script) to Japanese standards.
Should I use ㎆ or MB?
Use MB in ordinary technical prose. A Japanese translators’ guide lists MB or メガバイト for memory capacity. Compatibility normalization, a text-cleanup process, can turn ㎆ into MB; keep the square for legacy text or fixed-width layouts.
Don't confuse it with
4Questions people ask
1Why does ㎆ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ㎆
㎆\3386Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.