Civil War Union Patriotic Envelope
Perhaps the artist is saying: the unlawfully held "material" are the ten states which the Confederate government is now holding. In a broader sense, the populations of those ten states are now just as enslaved as the black slaves fleeing north to find freedom. The cover's statement "I'se contraband" becomes a cry for help to Northern brethren to come and set their Southern brethren free from the oppressive secessionist government that really has no right to hold power over these ten states. In a sly slap at the supporters of the Confederacy in these ten states, the artist is saying "you really do not realize what's happening to you. . . you need to be set free just like the black slaves that are coming north to find their freedom".