A badge is presented to indicate some feat of service, a special accomplishment, a symbol of authority granted by taking an oath, a sign of legitimate employment or student status, or as a means of identification. It serves as both an identifier and an acknowledgment of a person's status within an organization or institution. Sensors, alarms, and motion detectors are devices primarily used to detect and alert in case of security breaches, not as identifiers.

A cipher is a method that transforms a message into a masked (encrypted) form and also provides a way to reverse the transformation (decrypt) to recover the original message. This aligns with the question's requirement of a method that can both mask and unmask the message.

Role-Based Access Control (RBAC) is the most suitable access control model for Mark's objective. In RBAC, access permissions are assigned based on the roles within an organization. Each role has specific permissions, and users are assigned these roles according to their job functions. This model allows for systematic and consistent access control, ensuring that users can only access the resources necessary for their roles, which aligns with Mark's requirement.

A digital signature is used to authenticate asymmetric keys. Digital signatures involve the use of cryptographic algorithms that employ both private and public keys. They verify the authenticity and integrity of a message or document, ensuring it has not been altered during transmission and confirming the identity of the sender.

IPsec VPN uses AES (Advanced Encryption Standard) and 3DES (Triple Data Encryption Standard) for encryption. AES is widely used for its efficiency and security, while 3DES is another robust encryption method although it's considered less efficient compared to AES. Therefore, these two encryption methods are correct as they are both applicable to IPsec VPN.