Diamond Operator
HTML Entity Browser Test:

U+22C4 is the Unicode hex value of the character Diamond Operator, which is categorized as "math symbol" in the Unicode 6.0 character table.

Unicode Character Information
Unicode Hex U+22C4
General Category Math Symbol [Code: Sm]
Canonical Combining Class 0
Bidirectional Category ON
Mirrored N
Unicode Character Encodings
Diamond Operator HTML Entity ⋄ (decimal entity), ⋄ (hex entity)
Windows Key Code Alt 8900 or Alt +22C41
Programming Source Code Encodings Python hex: u"\u22C4", Hex for C++ and Java: "\u22C4"
UTF-8 Hexadecimal Encoding 0xE28B84
1 To type a Unicode symbol in Windows, hold down the ALT key and enter the decimal or hexadecimal code provided using the numeric keypad. The decimal alt code (Alt 8900) will only work on computers with support for this Unicode character in the active code page. The hexadecimal alt code (Alt +22C4) will work for all Unicode characters provided Hex input from the numeric keypad is enabled.
* If the Diamond Operator character does not display correctly in your browser, you may not have a Unicode font on your system that supports this particular symbol.