Is there a small river, or was there a river before?
Also there must be an old well. This is marked by the circle.
Also, measure the sides of the pointing arrow (for examle 4cm and
5cm) and either add them (4+5=9), or multiply them(4X5=20), and what you find is distance in steps, in the way the arrow points.
Where the arrow points, you should find information sending you
back the other side of the river, where the 'X' is.
Well, that's only my theory.
P.S. Get a good torch next time you search at night, and cover the most of the front, so no one else can spot you, from the light reflections.
Have a nice search.
The first picture looks like a skull with an eye patch. Could represent a concealed tunnel above ground and a trail that leads away from a marker to a shoulder site? Nice find.