The location of this particular set of carvings (west edge of Silver City, NM) was chosen to form a nearly perfect 45/45/90 triangle on cardinal coordinates with two other monumental landmarks in the area (14.5 mile-long hypotenuse). This triangle contains other perfect triangles inside itself at key geometrical nodes, all designated by other man-made signs. It's my opinion that the symbols used for the carvings, whether 'Egyptian', 'Hmong', etc. contain no messages per se, but are only used because they are easily recognized by those who are seeking them. If I had the resources, I would be mapping the location of similar panels (a couple dozen have been found) in relation to other regional landmarks, carvings, etc.
The Hmong board may have been used by the carvers as a guide or template. It's my opinion that these carvings were done within the past 100 years, very possibly in the 1930's.