1.5" Helmet numbers. Dye Cut in red with a white outline. The cost is per digit. These are an "ADD ON FEATURE" to any apparel or hat order. 
 
From the Manufacturer:
 
Die Cut Helmet Number Decals identify your players’ helmets and give a professional look.
Die Cut Helmet Numbers also improve the look of your helmets drastically.   Helmet Number Decals can be placed on the back, sides or front of the helmet.