What does HYF stand for?

Hayfields - Papua New Guinea - Airport symbol (OAG)

Hong Kong and Yaumati Ferry (SAUS)

Humbligny - France - Seismograph station code, US Geological Survey (SEIS)

Hydrofoil (SAUS)

Hyside Inflatables, Kernville, CA - Manufacturer code for watercraft hull identification number (USCG)