We don't use them, but many other operators around here do. Makes distingushing between multiple copies of the same machine easier, for record keeping and such. Back in the 70's, we used to BRAND ours, with a hot iron. Crazy. In any case, a HUO machine would never have one unless it was numbered accidently by the company that provided it. Could happen, but it's about 100 times more likely that it's not HUO.