It is illegal to spit on any public sidewalk or public conveyance.

The Law

Spitting on the sidewalk, in a bus, or on a train platform is an explicit violation of public health statutes. This law was aggressively enforced during the tuberculosis epidemics of the late 19th and early 20th centuries to prevent the airborne spread of the deadly disease. While rarely enforced today, it technically remains a punishable offense.