It's only approved by the mint but it isn't printed directly on the money. Then it would be fake. It is a custom label. That's why it is spendable. They also make the Easter bunny. It use to be on the 2 dollar bills.
I usually do for normal auctions. But I do the silly little phrases for the weird auctions.
.39 is first class mail. That's high? If a person wants to have it sent priority it can be.