Question: Why do Unicode code points appear as **`U+`**`<codepoint>`?

For example, `U+2202` represents the character **∂**.

Why not `U-` (dash or hyphen character) or anything else?

Answer: 
The characters “U+” are an ASCIIfied version of the MULTISET UNION “⊎” U+228E character (the U-like union symbol with a plus sign inside it), which was meant to symbolize Unicode as the union of character sets. See [Kenneth Whistler’s explanation in the Unicode mailing list](http://unicode.org/mail-arch/unicode-ml/y2005-m11/0060.html).
It is just a convention to show that the value is Unicode. A bit like '0x' or 'h' for hex values (`0xB9` or `B9h`). Why `0xB9` and not `0hB9` (or `&hB9` or `$B9`)? Just because that's how the coin flipped :-)