Privacy and warrants to obtain information
Your warrant just needs a simple digital signature, which provides the properties of authenticity and non-repudiation. That is very basic. Of course you need a proper public key infrastructure (PKI) along that, to ensure that everyone actually knows which verification keys are real, etc.

Regarding your different authorization levels, you might want to look into Mandatory Access Control, which then needs to be fulfilled by the PKI. But instead of granting access, you use it to decide which certificates are signed within the hierarchy. I guess you are looking for a compliance solution here, not a fancy technical solution, which might not have a mature implementation.

In general, this question is actually not about cryptography (at most about the application of cryptographic standards) and might be better suited for security-SE.