Greek Capital Letter Sigma
HTML Entity Browser Test:

U+03A3 is the Unicode hex value of the character Greek Capital Letter Sigma, which is categorized as "uppercase letter" in the Unicode 6.0 character table.

Unicode Character Information
Unicode Hex U+03A3
General Category Uppercase Letter [Code: Lu]
Canonical Combining Class 0
Bidirectional Category L
Mirrored N
Lowercase Version U+03C3
Unicode Character Encodings
Greek Capital Letter Sigma HTML Entity Σ (decimal entity), Σ (hex entity)
Windows Key Code Alt 0931 or Alt +03A31
Programming Source Code Encodings Python hex: u"\u03A3", Hex for C++ and Java: "\u03A3"
UTF-8 Hexadecimal Encoding 0xCEA3
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 0931) will only work on computers with support for this Unicode character in the active code page. The hexadecimal alt code (Alt +03A3) will work for all Unicode characters provided Hex input from the numeric keypad is enabled.
* If the Greek Capital Letter Sigma character does not display correctly in your browser, you may not have a Unicode font on your system that supports this particular symbol.