Code Signing?

Hi,
My apps will be for both Windows and OS X, and I would like both versions to be code signed.
Just curious if there is one company which will code sign both OS X and Windows apps, or, if I need the official Apple developer certificate for OS X and a different certificate for Windows apps?

I am only going to sell my apps through my website.

Thank you all in advance.

Yup… OSX Gatekeeper I believe recognizes only Apple issued certs… not 100% about Windows.