Soliciting, Disturbing the peace(Last one only when he blocked a town member).
The Liaison has the potential to be one of the most powerful roles a Triad can utilize. Essentially an Escort affiliated with the Triad, they have the ability to block one player every night, preventing them from using their night ability.
In general, blocking a random player every night until an Investigator or Sheriff claims is accepted play. However extreme caution should be exercised when a Serial Killer is in play with the ability to kill role-blockers at night.
Once an Investigator or Sheriff has claimed they should be the primary target for role-blocking as they are extremely difficult to kill until all Doctors have been killed.
Secondary targets for role-blocking are killing roles such as Serial Killers (when the ability to kill role blockers is disabled) and Vigilantes as they have the potential to kill off the Triad at night. Arsonists should also be blocked if you can accurately determine who they are.
If you hope to credibly claim Escort later on in the game, it is not advised to role block a single person continuously, even if they aren't a Sheriff or Investigator. A normal Liaison would not do this due to fear of interfering with a Town role.