IBM documentation refers users who are wanting to create custom signatures to the Signature Community at http://bigfix.me/signature. The last posts there were 12-18-2018. Is this the active signature community?
Below is one of the references under “Expanding the custom software catalog”:
“Before you create custom signatures, check the signature community. It is a place where you can find custom signatures that are created by members of the community. You can download such signatures and import them to BigFix Inventory. After you create your custom signatures, consider contributing the community.”