how do i get a tick symbol

You can use Nevin Mrgan's web app glyphboard. Read this article about using the iPhone's alternate keys and how to use the gyphboard. http://www.iphonejd.com/iphone_jd/2010/03/typing-letters-or-symbols-that-are-not -on-the-iphone-keyboard.html

As in a checkmark? option+v = √

That will only work with a hardware keyboard, though.

Other than that, it looks like you're limited to copy-pasting it from a website, such as Wikipedia.