Yes, on my 590A1 it is stamped "M590A1" on the left side of the receiver. I don't have a picture of my own to share but it looks like this: http://deviating.net/words/wp-content/uploads/2013/05/original.jpg

Aaron, my 590A1 is not. It is stamped on the metal receiver on the underside in front of the tube load gate (Mossberg Made in USA North Haven, Conn 590 12 GA). Since I have owned my 590A1 for many, many years, I would verify with Mossberg Customer Service at U.S. (800) 363-3555 | 8:00am-4:30pm Eastern or by online inquiry here : mossberg.com/contact-us/