I'd check the red rectangle with the white circle inside first, to see whether there is some kind of site.
Red circles for places to check metal detecting, for mostly loose coins/treasure or artifacts of value, from surface down to 1-2 feet deep.
Red line box for very deep coins/treasure or artifacts of value.
Green in general is a color indicator, I use for various other targets mostly archaeological (old ruins or foundations but especially those non-metallic objects such as Indian flints, glass, pottery, carved stone with treasure signs).
Purple line box for paranormal type sites, including tombs, ancient religious artifacts, temples, spirits, and burial grounds.