What you describe is not DRM. The system you describe can be part of a DRM scheme, but verifying signatures itself is not a copy prevention measure. I'm pretty

What you describe is not DRM. The system you describe can be part of a DRM scheme, but verifying signatures itself is not a copy prevention measure. I'm pretty sure the types of DRM that are being referred to here are the kinds that hide a secret key in a "black box" on the consumer's device, and then sell the consumer content that can only be decrypted by that black box.