One of the original theories proposed by Dixon Spendlove in 1998, was that these marks were used by the ancients to trap or snare eagles, hawks and other raptors to acquire the sacred feathers they  needed for religious ceremonies.

While Hollywood has shown us instances of young braves scaling sheer canyon walls to steal feathers from the nests of eagles, such things are completely removed from reality.

Dixon observed that many of the glyphs, were located on or near the edge of mesas, cliffs or buttes which  are great hunting locations for birds of prey. Several of the glyphs were situated in such a way that they would allow a man an excellent hiding position over the edge of the precipice.

A man could conceal a strong cord in the groove of long line of the glyph...  following the circle to make a loop for a snare...   and place a small rodent or sparrow, tethered to a rock or weight in the hole inside the circle...   Then wait out of site over the edge of the precipice....  Allowing the foundering animal to act as bait for any passing raptors.

The Hopi have demanded, by legal action, their religious right to trap eagles and hawks from "traditional locations on lands that are now used by  Navajos and other tribes. Why not just use any hilltop available to them?  The Hopi reservation has more than enough suitable mesas... 

Unless, there was something special about a particular hilltop... Something that made it a sacred site...  Something that marked it as Holy.

While not all the glyphs could be used for this purpose, a surprising number of them would work nicely for this purpose. Again, in an amazingly odd coincidence, the   Paleo-Hebraic theory lends support to this idea...

The Hebrew letter Kolph  written in it's original Paleo-Hebraic form is  , ...And it's Notarikon ideogram is noose or snare.