The title of this article is a conjectural. Though the topic is found within The Simpsons universe, a proper name is not available.
The Sirloin Staff are waiters who work at The Singing Sirloin. They sing at their customers songs depending on the occasion. One of them is called Mary Kay and she is at the front door of the restaurant aware for customers who want to escape, like when the Simpsons were getting away to not pay and the waiters sang "They're getting away, stop them Mary Kay!".
They have sung an anniversary song to Mr. and Mrs. Winfield, a pregnancy announcement song to a couple, a funeral song to some people, a birthday song to Marge and a "Happy First A" song to Bart.