For best results, you can forgo the paper tabs entirely and bend the wire into a handle shape and float the island on wires that won't even appear when you go to spray paint your image. I did this for the islands where it mattered most, like in one of the logos where it would matter most that it look clean and professional.
I found the paper tabs to be acceptable and a time saver on the letters and numbers since the eye is more accustomed to seeing stencil tabs in fonts.
More info on making floating islands in stencils can be found in Fungus Amungus' classic Stencils with Islands - Pt. 2 Instructable.
Step 1: Start With an Image
Take a look at it, does it have floating islands? Like the white circle inside the "a's", "o" and "g"?
If it does, proceed.
Step 2: Draw Rectangles to Create Tabs
The width is up to you, pick a value that's both structural, but not so wide that you'd notice it at first. 3/32" is around what I used.
This creates tabs which will hold the island in place. Two tabs are sufficient for small islands, but if the island is really big, make more.