I'm hoping these links will translate. Two examples of how the power button relates to shooting images.
The first image shows how the power button resembles the open end of a pistol barrel.
http://comps.fotosearch.com/comp/ARP/ARP124/gun-barrel_~cp_gunbarrel.jpgAlso, the power button can resemble a top-down or bird seye view of a standard shooting stance.
http://img.redwolfairsoft.com/upload/bullet/69/WEA-TOP-L.jpgplease advise if you have any questions.