Preparing for some upcoming audits, I noticed one of the checkpoints was to ensure each ESXi host was configured with a warning banner stating the machine is being monitored and audited when someone logs into the ESXi host via SSH. This type of message is something you see on most any company or government computer before you login.
There are two message types that can be used to achieve this, the first being login banner (/etc/issue) and MOTD (/etc/motd). The difference between the two are where they are shown. The login banner is shown between the username and password inputs during login, while the MOTD is displayed after a user has successfully logged into SSH.