In FNMS Cloud, there is a Sign out button on top right corner of FNMS UI but not in place for FNMS on-prem releases.
With FlexNet Manager Suite On-premises (without SAML being configured), authentication of HTTP connections to the web server is typically configured to use Windows Authentication. When a web application (like FlexNet Manager Suite) authenticates users using Windows Authentication, there is no concept of a "sign in" or "sign out" operation at the application level - the sign in/out is done to your Windows login session. When Windows Authentication is used to authenticate to FNMS, your login session is tied to your Windows login session: there is no concept of "login" or "logout" as it applies to FNMS. They only way to "logout" is to log out of your Windows login session, which you would typically do through the Windows Start menu, not through an individual application.
Logout feature is available for FNMS On-premise with SAML setup. The logout link will be displayed when the operator is authenticated via Forms Authentication.