Is there a "n/a" symbol in unicode?

For future reference, the fastest way I know to answer questions like the OP's when I have them myself is to go to unicodelookup.com, because of the way it works: there's a search bar at the top, and you just type a string and it will return any and all unicode characters containing that string (this is also a great way to discover new and useful symbols). So in the OP's case, he could proceed like this:

• first try entering "not" (without the quotes) in the search field
• visually scan through the results... doing so would not reveal a "not applicable" character in this case
• try again but this time entering "applic" in the search field
• again, doing so would not turn up anything along the lines of what he's looking for

At that point he would be reasonably confident the current Unicode standard does not have a "n/a" symbol.

If you use Firefox you can define a keyword like "uni" to search that site from the URL bar, meaning any time the browser is open and regardless of what page or site is currently showing, you could do this:

• hit [F6]... this moves the cursor to the URL bar at the top
• type something like "uni applic" and hit [Enter]... this brings up the unicodelookup.com website with the search results for "applic" already showing

For the above to work you would need to define your keyword ("uni" or wtv you prefer) to point to location http://unicodelookup.com/#%s.

There's a Negative Acknowlege icon...

␕ symbol for negative acknowledge 022025 9237 0x2415 ␕

Found by searching negative on the Unicode Lookup site.

I'm not a fan, and for my purposes have just gone with __N/A__ (Markdown..)

Looking at the Unicode code charts, I do not see a single N/A symbol. I do, however, see ⁿ (U+207F) and ₐ (U+2090), which you could separate with / (U+002F) eg: ⁿ/ₐ, or ̷ (U+0337), eg: ⁿ̷ₐ, or ̸ (U+0338), eg: ⁿ̸ₐ. Probably not what you are hoping for, though. And I don't know if "common" fonts implement them, either.