Yep, this exactly how I spend my workday at Post Office.
Okay maybe not.
Here at my post office there seems to be a lot more whining going on than singing and I seriously doubt we have anyone with the musical talent or dexterity to pull off that type of letter canceling. Good thing we don't since my job is actually to keep the machines that cancel the mail running. Then again, machines are not nearly as entertaining as that fellow.