Unicode has several notable examples you can simply copy and paste into a string declaration in Xcode, or use the standard Unicode String Escape (\uxxxx) and iOS is actually quite fluent when it comes to Unicode (I know some of the char’s are fairly ugly, but that’s Unicode for ya’):
Unicode Character ‘GEAR WITHOUT HUB’ (U+26ED): http://www.fileformat.info/info/unicode/char/26ed/index.htm
Unicode Character ‘GEAR’ (U+2699): http://www.fileformat.info/info/unicode/char/2699/index.htm
Or prepare an image and set the UIBarButtonItem’s customView property accordingly.