Upper middle looks like a plug in a mouth, upper left and right looks like a mouth that indicates direction, lower left looks like a tunnel symbol, sides may indicate depth, there may be another 2 other corners that shows a triangle, if so it is a very important to get the direction and directions off of everything on the corners, Also there may be a horzional tunnel symbol, and a " 0 " and a uoside down U could be O = 15 and U = 21