The white line box with the arrow represents a possible void signal. The others are unidentified type signals. Here is from my file of definitions of possible targets. Red can be almost anything related to treasure hunting, hopefully something of value.
White in general is a color indicator, I use for natural caves or man made tunnel entrances and mine shafts, other similar type excavations (including old wells, tombs, etc.).
Red circle is to mark areas, of loose or surface coins/treasure and artifacts of value, down to 1-2 feet deep.
Red line box (or solid filled circles) 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).