Are the police all plainclothes when they go to the hotel for rounds?

Not all of them. The police went to the hotel for investigation reasons. When performing rounds, they wear clothes including plain clothes and uniforms. The police refers to the police organs and their personnel established by the state and its rulers according to the will of the state and the ruling class, and also refers to the national public officials who exercise police power and perform police duties in the police organs according to the armed nature of safeguarding national security and social order.