If it is an older Merc, the data plate will be attached to the swivel tube and you will be able to see it from the front as you look between the transom clamps which attach the engine to the boat. As well some data plates were attached to the rear side of the swivel. Newer engines have a cheap sticker which has a tendency to disappear. Also you can look on the lower right side of the powerhead for a disc like this:
