Cybercriminals know that “free serial number” is a high-volume search term. They create fake pages with downloadable keygens or text files containing “working” keys. Inside those downloads can be:

: Located on a card labeled "Product Key" with a yellow sticker, or on the back of a magnet inside the sealed software bag. Physical Disc Case

If you're looking for free or low-cost alternatives to SignMaster, consider:

The Product Serial Number (PSN) is a unique issued at the time of purchase. Unlike older software that used physical USB dongles, modern versions of SignMaster use this digital key to activate the software online or offline. The Reality of "Free" Serial Numbers