The FCC field bureau investigates recreational boater use of their VHF Marine Band radio, and they do investigate, locate, and prosecute rule violators. The FCC regulates many radio services, many of them commercial services, which seem to have a higher priority.
A Florida man thought it would be fun to use a marine radio in his car. Fined $20,000. See
https://apps.fcc.gov/edocs_public/attac ... -232A1.pdf
A Tennessee man was fined $17,000 for malicious interference to the Marine Band. See
http://www.arrl.org/news/fcc-upholds-17 ... nessee-ham
An interesting case was a retail automobile dealer who decided he would use the General Mobile Radio Service as a radio system for his business without obtaining a license. He was fined $10,000. See
http://www.radioworld.com/business-and- ... ler/303105