If you have a Business or Enterprise level of service, you have access to the Approver role when configuring the agreement.
Approvers are not required to apply a signature, so one is not programmatically added (like the Signer role does).
However, if a field is added to the document for the approver, then they do have the authority to fill in that field. Meaning, you can add just an initials field, and as long as it's Required per the field properties, the recipient will have to apply their initials.
The downside to this is the history and audit report will reflect this recipient as an Approver instead of a Signer. I don't know the nature of your documents, so this may or may not be acceptable.