Usually challenge coin in round shape with 2D or 3D designs 1 side or 2 sides.there also have some irregular shape challenge coin in square shape,cut out design...
On all design,i think the most useful design is challenge coin bottle opener.for example,below antique silver challenge coin bottle opener.
The bottle opener design is perfectly based on eagle's mouth.
What's more Awards Gift CO.,LTD also make challenge coin with bottle opener in cut out design,like below photos.
Custom design welcomed,please feel free to contact us: firstname.lastname@example.org