The auditor should be most concerned about the information security policy not being approved by the policy owner. This is because the policy owner is the person who has the authority and accountability for ensuring that the policy is implemented and enforced. Without the policy owner's approval, the policy may not reflect the organization's objectives, risks, and compliance requirements. The policy owner is usually a senior executive or a board member who has a stake in the information security governance. The other options are less critical than the policy owner's approval, although they may also indicate some weaknesses in the policy development and maintenance process. References:
* CISA Review Manual (Digital Version), Chapter 1, Section 1.21
* CISA Online Review Course, Domain 5, Module 1, Lesson 12

Referential integrity is a property of data that ensures that all references between tables are valid and consistent. Disabling referential integrity controls can result in orphaned records, data anomalies, and inaccurate queries. The most effective way to compensate for the lack of referential integrity is to perform periodic table link checks, which verify that all foreign keys match existing primary keys in the related tables.
More frequent data backups, concurrent access controls, and performance monitoring tools do not address the issue of data consistency and accuracy. References: ISACA CISA Review Manual 27th Edition, page 291

The most significant concern for an IS auditor when reviewing an industrial control system (ICS) that uses older unsupported technology in the scope of an upcoming audit is that there is a greater risk of system exploitation. System exploitation is an attack that occurs when an unauthorized entity or individual takes advantage of a vulnerability or weakness in a system to compromise its security or functionality. System exploitation can cause harm or damage to the system or its users, such as data loss, corruption, theft, manipulation, denial of service (DoS), etc. An ICS that uses older unsupported technology poses a high risk of system exploitation, as older technology may have known or unknown vulnerabilities or defects that have not been patched or fixed by the vendor or manufacturer, and unsupported technology may not receive any updates or support from the vendor or manufacturer in case of issues or incidents. Attack vectors are evolving for industrial control systems is a possible concern for an IS auditor when reviewing an ICS that uses older unsupported technology in the scope of an upcoming audit, but it is not the most significant one. Attack vectors are methods or pathways that attackers use to gain access to or attack a system. Attack vectors are evolving for industrial control systems, as attackers are developing new techniques or tools to target ICSs that are increasingly connected and complex. However, this concern may not be specific to older unsupported technology, as it may affect any ICS regardless of its technology level. Disaster recovery plans (DRPs) are not in place is a possible concern for an IS auditor when reviewing an ICS that uses older unsupported technology in the scope of an upcoming audit, but it is not the most significant one. DRPs are documents that outline the technical and operational steps for restoring the IT systems and infrastructure that support critical functions or processes in the event of a disruption or disaster. DRPs are not in place, as they may affect the availability and continuity of the ICS and its functions or processes in case of a failure or incident. However, this concern may not be related to older unsupported technology, as it may apply to any ICS regardless of its technology level.
Technical specifications are not documented is a possible concern for an IS auditor when reviewing an ICS that uses older unsupported technology in the scope of an upcoming audit, but it is not the most significant one. Technical specifications are documents that describe the technical characteristics or requirements of a system or component, such as functionality, performance, design, etc. Technical specifications are not documented, as they may affect the understanding, maintenance, and improvement of the ICS and its components. However, this concern may not be associated with older unsupported technology, as it may affect any ICS regardless of its technology level.

A digital signature is a specific type of e-signature that is backed by a digital certificate. A digital certificate is a document that contains the public key of a signer and is issued by a trusted third party called a certificate authority (CA). A digital signature provides proof of the identity of the signer and the integrity of the signed document.
A characteristic of a digital signature is that it is unique to the message. This means that a digital signature cannot be copied from one document to another without being detected as invalid. A digital signature is created by applying a mathematical function called a hashing algorithm to the document. A hashing algorithm produces a fixed-length output called a hash or digest from any input data. The hash is unique to the input data; any change in the input data will result in a different hash.
The signer then encrypts the hash with their private key (a secret key that only they know) to create the digital signature. The encrypted hash is attached to the document as the digital signature. The recipient of the document can verify the digital signature by decrypting it with the signer's public key (a key that is publicly available and matches the private key) to obtain the hash. The recipient then applies the same hashing algorithm to the document to generate another hash. The recipient then compares the two hashes; if they match, it means that the document has not been altered and that the signer is authentic.
Therefore, a digital signature is unique to the message because it is derived from the hash of the message, which is unique to the message.
References:
* 7: Free Online Signature Generator (Type or Draw) | Signaturely
* 8: What are digital signatures and certificates? | Acrobat Sign - Adobe
* 9: eSign PDF with Electronic Signature Free Online - Smallpdf

The audit team's most important course of action is to consult the legal department to understand the procedure for requesting data from a different jurisdiction, as this will ensure that the data analytics techniques are compliant with the applicable laws and regulations of both countries12. Requesting data from a foreign branch may involve legal risks such as data privacy, data sovereignty, and data protection34, and the audit team should seek legal guidance before proceeding with the data extraction and analysis.
References
1: Data Analytics and Auditing Standards 2: Data Analytics and the Audit Process 3: Data Privacy and Data Protection: US Law and Legislation 4: Data Sovereignty: What It Is and Why It Matters