Answer: Copperheads. http://ohiohistorycentral.org/w/Copperheads
"Their opponents nicknamed them Copperheads, describing the opponents of the war as poisonous snakes waiting to strike a blow in favor of the South. The first reference to "Copperheads" in Ohio occurred in 1861. Accepting the Copperhead name, many opponents of the war began to use the portrait side of copper coins as badges and tokens for identification and promotion of their cause."