Before revision: For a current source that is not contained between two meshes , the mesh current will take the positive or negative value of the current source depending on if the mesh current is in the same or opposite direction of the current source.
After revision: (for example, the current source in essential mesh 1 in the circuit above)For a current source that is not contained between two meshes , the mesh current will take the positive or negative value of the current source depending on if the mesh current is in the same or opposite direction of the current source.