Remove their keyboard and leave a note
At most companies, it is irresponsible for IT to allow unlocked PCs and terminals. Most have a security policy in place and many demand that this action take place and be verified. Many security officers roam the halls, confiscating keyboards (after locking the screen) and leave a note for the employee. The note requests that they contact their manager to setup a meeting with security to receive additional coaching about security -- and then they get their keyboard back.