Tree Markings

Hello all.  One of the properties I've been metal detecting on has a wooded area and cleared field.  I've found several symbols on the property in the wooded area that leave you with the feeling that there is something there to find.  On the property amongst lots of other trees that have symbols (some of them I'm sure is just graffiti).  Ive found this tree which has a hoyo in it, looking through that tree in one direction and following that path, there is another tree that has all kinds of markings on it.  There is also there is another tree that has a similar symbol on it.  All 3 have a U that has another letter inside the U.  One tree has an M in the U, the hoyo tree has D in the U and the tree with all kinds of symbols on it has an H in the U.  Anyway, I don't know if this has any signifigance or not, but thought I should go ahead and post them together because of that similarity.  I would really appreciate any input that can be given on these. Thanks for any help you can provide.

Thanks Shortstack and poorfarm for your posts about the Hoyo tree!

Hoyo Tree D inside U and other symbols:




Multiple Symbol Tree H inside U and lots of other symbols (last picture has the U with the H in it):






Other Tree M inside U no other symbols:



Positions of the Trees (this isn't exact, but to give you an idea anyway):

If it was me, I'd go to the center and Dig like Hellllllllllll

Thanks Gunrunner61!  I hope it's that simple  , but there are so many symbols on the property, I've been kind of running in circles and beating my head  with nothing to show.  I'm kind of scratching my head at this point  .  I have metal detected there to what I thought was the center of those trees and in between those trees, but at the same time from what I've read, some things may be buried really deep (10ft +), so a metal detector may not pick anything up.  And at the same time I can't just go around digging 10ft holes  or even 3 or 4ft holes around the property without feeling confident that that's the spot, the owner probably would not take to kindly to that  .  I think the fact that they have a similar symbol on them is saying hey pay attention to me, but I guess I'm not sure what it's trying to tell.  In this post I've included another picture of the tree positions with the angle indicated of where I took the picture.  I labeled each picture 1, 2, 3, etc in relation to how they appeared in the post.  Please let me know if I'm confusing the issue as I sometimes get to caught up in unimportant details  .

Thanks for your help and thanks to those who post in these forums.  I'll learn alot more here than I have in any book .