Section 31. Such person or corporation shall plainly mark each pole, pier, abutment or other fixture supporting wires or cables containing wires over streets or buildings with the name or initials of the owner of such pole, pier, abutment or other fixture. Wherever cross arms or other appliances for the support of wires or cables belonging to different owners are attached to the same pole, pier, abutment or other fixture, every such cross arm or other appliance shall plainly be tagged or marked with the name or initials of the owner thereof. Wherever wires or cables belonging to different owners are attached to the same cross arm or other appliances for the support of wires or cables, every wire or cable shall be tagged or marked with the name or initials of the owner at or near its point of attachment to such cross arm or other appliance. No such tag or mark shall be required for the wires, poles, piers, abutments and other fixtures of a street railway or electric railroad company, except for its feed wires supported by poles carrying wires or cables belonging to another owner, and for its poles supporting wires or cables belonging to another owner, and for poles belonging jointly to the street railway company and another owner.