This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is not a composition. Its East Asian Width is wide. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. U+3012 offers a line break opportunity at its position, except in some numeric contexts. The glyph can be confused with one other glyph.
The Wikipedia has the following information about this codepoint:
〒 (郵便記号, yūbin kigō) is the service mark of Japan Post and its successor, Japan Post Holdings, the postal operator in Japan. It is also used as a Japanese postal code mark since the introduction of the latter in 1968. Historically, it was used by the Ministry of Communications (逓信省, Teishin-shō), which operated the postal service. The mark is a stylized katakana syllable te (テ), from the word teishin (逓信（テイシン）, communications). The mark was introduced on February 8, 1887 (Meiji 20.2.8).
Representations
System
Representation (click value to copy)
Nº
12306
UTF-8
E3 80 92
UTF-16
30 12
UTF-32
00 00 30 12
URL-Quoted
%E3%80%92
HTML hex reference
〒
Wrong windows-1252 Mojibake
〒
Encoding: BIG5 (hex bytes)
A2 45
Encoding: BIG5HKSCS (hex bytes)
A2 45
Encoding: CP932 (hex bytes)
81 A7
Encoding: CP950 (hex bytes)
A2 45
Encoding: EUC_JP (hex bytes)
A2 A9
Encoding: EUC_JIS_2004 (hex bytes)
A2 A9
Encoding: EUC_JISX0213 (hex bytes)
A2 A9
Encoding: GBK (hex bytes)
A8 93
Encoding: GB18030 (hex bytes)
A8 93
Encoding: ISO2022_JP (hex bytes)
1B 24 42 22 29 1B 28 42
Encoding: ISO2022_JP_1 (hex bytes)
1B 24 42 22 29 1B 28 42
Encoding: ISO2022_JP_2 (hex bytes)
1B 24 42 22 29 1B 28 42
Encoding: ISO2022_JP_2004 (hex bytes)
1B 24 42 22 29 1B 28 42
Encoding: ISO2022_JP_3 (hex bytes)
1B 24 42 22 29 1B 28 42
Encoding: ISO2022_JP_EXT (hex bytes)
1B 24 42 22 29 1B 28 42
Encoding: SHIFT_JIS (hex bytes)
81 A7
Encoding: SHIFT_JIS_2004 (hex bytes)
81 A7
Encoding: SHIFT_JISX0213 (hex bytes)
81 A7
Adobe Glyph List
postalmark
digraph
=T
RFC 5137
\u'3012'
Bash and Zsh inside echo -e
\u3012
C and C++
\u3012
C#
\u3012
CSS
\003012
Excel
=UNICHAR(12306)
Go
\u3012
JavaScript
\u3012
Modern JavaScript since ES6
\u{3012}
JSON
\u3012
Java
\u3012
Lua
\u{3012}
Matlab
char(12306)
Perl
"\x{3012}"
PHP
\u{3012}
PostgreSQL
U&'\3012'
PowerShell
`u{3012}
Python
\u3012
Ruby
\u{3012}
Rust
\u{3012}
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