Unicode has a million icon-like glyphs, but they're not always easy to search by, since I don't always know what they look like.
Is there a Unicode glyph that looks like a "key"? Or is there a symbol that's used in database circles to mean "primary key", which is in Unicode?
I've found Google to be the best way to find Unicode characters. I didn't find see anything useful for a key symbol, however.
If you want to search visually, use the PDF charts, since HTML-based listings will only show symbols that occur in the particular set of fonts you have installed.
Lacking any specific symbol, I would just use "I" to indicate an index and "PK" for a primary key.
Check that question: what-unicode-character-do-you-use-in-your-website-instead-of-image-icons
in a word, better way is use icon, there is a lot of free icon on the internet. (i like that: http://www.freeiconsdownload.com/Free%5FDownloads.asp?id=61)
I browsed through all the symbols (using a PHP script I created a while back) and can't see a key symbol. You could try one of these:
A mathematic-looking P:
ℙ (#8473)
Various star shapes:
★ (#9733)
☆ (#9734)
✶ (#10038)
There doesn't seem to be a unicode character that fits your description, but I'd recommend the silk icon set by famfamfam if you can use icons in your situation--just a suggestion :P
I used a little Python 3 script to look, and the closest I found does not display here for me (does display in Idle on my machine), but it is:
9897 ⚩ HORIZONTAL MALE WITH STROKE SIGN
(Looks like a male sign pointed right with a perpendicular stroke added between the arrow and circle)
I searched for various matches like "KEY" and "LOCK" in the unicode names using Python's unicodedata module and no luck there.
Editing to add - Ah hah - one that looks even more like a key:
9911 ⚷ CHIRON
I give both of the above code points in decimal. To see them and their hex codes, go to this link:
http://www.unicode.org/charts/PDF/U2600.pdf
See 26B7 in particular for the Chiron.
Check out #26bf.
9919 ⚿ SQUARED KEY (HTML: ⚿)
It's the parental lock, which is a key inside a square. It's a newer Unicode specification so standard fonts don't support it, but if you can find a font that has it, you're home free.