Yup, a medal. Commemorates the Buffalo Soldiers, a black only regiment of the Union Army during the Civil War. More on the Buffalo Soldiers here: http://en.wikipedia.org/wiki/Buffalo_Soldier, http://www.buffalosoldiers-amwest.org/history.htm and here:
I think its a challenge coin. I could not find the exact same one, but a similar one was going for 16.
Agreed, I think it is a challenge coin. The buffalo soldiers were based there for a bit so the motto is probably just a reference to that history. Challenge coins are cool to collectors but I don't know that they worth anything money-wise.
Ditto, it's a challenge coin. As far as worth...you'll have to find the right person to sell it too in order to get the most for your money. I'd say the value is between $5 - 30. Challenge coins can go for a bit more to the right collector, but it could take quite a while to find that collector.