I’ve been going crazy over that Mac OS X has a shortcut for (Square root sign) but not for (Check mark).

The shortcut is ⌥+v.

Today I learned that you can change the default keybindings for such things, and it works in almost all applications. You only need to create the file DefaultKeyBinding.dict in ~/Library/KeyBindings (You might have to create that folder as well) and fill it with:

  "~v" = (insertText:, "✔");

Voilà - you can now use ⌥+v to create .

Of course you can do much more than just adding a shortcut for as seen in this article from Harvard: Usable Selectors for Cocoa Key Bindings