Challenge coins were traditionally given in the military to prove membership when challenged and to enhance morale. They are given in recognition of special achievements by a member of their group. Since then, other organizations such as fraternities/sororities, biker groups, or even movie sets have given them out in recognition of certain services or accomplishments.
We offered challenge coins during our previous two Campaigns, Lazer Team the movie, and Million Dollars, But… the Game to give backers a way to show that they helped fund and support our endeavors. For RWBY: Combat Ready we are offering the coin again, letting Backers know that they are part of a massive community-wide event. (Lazer Team’s Coin: http://imgur.com/mtke97Z for example.)