There is no single universal "serial number" for Metal Slug PC games in the way there is for a piece of software like Windows or Adobe Photoshop. Instead, the "serial number" collectors look for is the printed on the box, disc, and manual.

If you have a physical retail copy of (released by DHM Interactive in 2009/2010), the serial number—often called a "CD Key"—is usually found in one of three places: