Hang onto it, as you will likely need it next year. 

Years ago I had a stamp made that said "HUH?" I still use it. I was particularly useful when the client received two letters from IRS. One said "Here is your refund" and the other said "We think you owe us ..." Both dated the same date and both from the same IRS center. I also used it on some client communications, but I seldom showed that to the client.