One of the easiest and cheapest ways to stencil the decals onto your armor is just find a font style you like on your computer type in the desired text then print it out on to some card stock. From there you can cut out the text and then tape it to your armor where you can either spray paint it or hand paint over the stencil. Its a pretty cheap and effective way to decal your armor just be sure you tape the stencil down so you dont get any seepage and mask off the area to prevent overspray.
Hope that helps man!