Haha, my current favorite band. They're really cool, sort of an acoustic irish folk band. Their voices are really operatic and beautiful. Sadly, they aren't incredibly popular, so you'd be hard-pressed to find an actual Smoke Fairies shirt. That being said, I took more of my homemade spraypaint and made a shirt of my own.
Cut out the shapes of whatever you want your shirt to say.
Put them down on your shirt. If you want to be sure that the paint doesn't bleed through, put something between the layers.
Take your homemade spraypaint (you HAVE to use that for this project, you can't use actual spraypaint) and spray directly down onto letters, not at an angle.
Once you've sprayed all you want to spray, take off your letters.
If you have any lace trim that you also want an impression of on your shirt, you can do that as well, but make sure to do a test run with it on a white piece of paper first.
Let it dry.