Hurst Industries Fiberglass Fenders and Hood

It does look more like "M" or "N" prefix but I found this:

Harstil Industries Inc
Boatbuilding and Repairing Companies
17150 15 Mile Rd
Fraser, Michigan 48026-3442

Founded in 1956, Harstil Industries Inc is a small organization in the boatbuilding and repairing companie