Found these markings just south of Miami near the bay. Legend has it that Black Caesar Burried 24 gold bars in the area. Check out the metal ring imbedded in the tree.
I doubt those trees are anything near 300 years old, and the marking are more than likely a combination of natural events and perhaps being used as an make-shift fence post. JMO.
Mirage is right, the trees shown are not very old. The tree in the top left photo grew up around the cord that is shown. Don't let this deter you, keep looking for that gold!