Actually, I'll have an orange hoodie, black pants, a hellspawn tattoo and the bandana over the mouth. He'll enjoy it.
In theory the way to spot a disguise is by having a dominant feature or color on your character. When you are killed you call out your feature/color to your team so that they know how to identify any potential operatives in disguise. If you run with the same group then you can each make sure that you have different features/colors to streamline the process. The alternative is the TF2 technique of simply firing your weapon when you enter a defensive position that your team is protecting.