Moen shower valves and parts are known for withstanding the test of time. According to Faucet Fix, Moen is the third most popular faucet brand in the United States. With that in mind, if you have an old home with a bathroom that has never been redone or refinished, there is a good chance that it has a Moen shower valve. But before you find replacement parts or update the valve, you need to make sure that it is a Moen--and there are three specific places where you need to look.
Look closely at the handle buttons that were attached to the shower valve. Typically, "Moen" will be written in the middle of the "Hot" and "Cold" buttons. If you do not see this, the handle buttons have been replaced, or the "Hot/Cold" button is a lever (wall escutcheon).
Look closely at the wall escutcheon. This is the plate around the "Hot/Cold" level that turns the shower water on. "Moen" will be written on the metal wall escutcheon plate surrounding the lever. If you do not see this, or the wall escutcheon has been replaced, there is one other place to look.
Remove the wall escutcheon and any handle buttons to view the valve body of the shower valve. "Moen" will be stamped on the side of the valve body on even very old shower valve models.