It seems like all the other information is set in the Config.daml file under the AddInInfo tag, but DigitalSignature is not being recognized. Not seeing any of the samples that have this line filled out either.Thank you.
This wiki has info on how to Digitally sign add-ins. If an add-in has a valid digital signature, the Add-In Manager will read this signature and provide that information.
ProGuide: Digital Signatures