If you don't want to tract your shirts in inventory, you have to set up your item "shirts" or whatever you track them by as a "non inventory part" in the "type" section. That way, it's not associated with an inventory item, but you can still track your income on shirts.
So, if you wanted to keep inventory on the letters/numbers but not the shirts, then you'd have to have separate lines on your invoice - one for the shirts, then one for each letter/number you put on the shirt.
Hope this helps
