Get a copy of Zaloga's "US Armored Funnies" Certain units used different designs. For instance, the top pic that Stikpusher provided is called the "Douglas Device" and was prominently used by the 3AD. The second set of prongs, mounted on an M5A1 Light tank, was the more widely used design.
Indeed, initial attempts included simple two sharpened logs, attached to the transmission cover bulges. The idea there was to ram two holes into a hedgerow, and then engineers would follow up by emplacing explosives. Some other early designs looked flimsy and not robust. What Viejo said is true initially. But it changed when Sgt Culin's ideas came forth did the hedgerow prongs really come into widespread use with a successful design.