I'm reopening this since the glyphs are drawn on the map again. 
I don't see anything on current aerial imagery (Esri, Bing). Apparently the glyphs were surfaced by a 2018 fire: https://coastmonkey.ie/eire-sign-bray-head/
But the new tagging of man_made=geoglyph + barrier=wall + height=0 seems contradictive to me and like tagging for the renderer. Sadly the mapper creating them has a habit of not writing any changeset comments.