I don't think we've ever seen decals for the U shaped decals. :facepalm You may have to handpaint them on with a brush.
OR, you could do what we did, and spray paint them on like how you would stencil.
First, draw a pattern for the U's on a piece of paper, cut out the U, tape the piece of paper on the helmet with the U and try and line it up right. Then spray on the paint, but be sure you have the rest of the helmet covered so you won't get paint on it.
Also, the paint seaped through the paper one time we did it, so you may want to do two layers of paper or a thicker paper.
Hope that makes sense but if it doesn't just say so, and we'll try explaining it a bit better.