It's been a while since I've heard it, but the detector in Biddeford announced itself as "Guilford Rail System" whenever I heard it (roughly from 1999 to 2002). When I lived in Wells, I was occasionally able to pick up the detector in North Berwick (from 2002 to recently) and it, too, always said "Guilford Rail System."
I've never had a chance to hear any of the detectors that announced themselves as "Boston & Maine Railroad," although I remember a web page that I came across a few years ago -- not sure if it still exists -- which had audio clips of various defect detectors, and one of the clips was of the B&M Hudson River Bridge detector. The voice on the detector sounded like he had a southern accent, which I thought was rather comical for a New England railroad.
Pan Am Railways — Boston & Maine/Maine Central — Delaware & Hudson
Central Maine & Quebec/Montreal, Maine & Atlantic/Bangor & Aroostook
Providence & Worcester — New England — GE Locomotives