Garrett atx pi 12+20inch coil, Garrett mh series, Garrett 2500+t-hound attchmnt, fisher tw-6 two box, Pulsestar pro ii with various coils up to 98 inches, pulsemaster pro w/1.2 m coil
there are a LOT more symbols, initials, dates as well so this isn't the only one. think dsty is right, at first I thought it was a fish, but after being out and about I think it is relating to a trail as well