That's not a RR horn. On the same side pictured there should be stampings with the Sparton name voltage, 12V or 6V, and possibly a date code. The two terminals must be positive and a ground, RR horns are case grounded. Sparton made horns from way back when that look like these, I have a 6V sparton horn here from the late 30's-early 40's that the case is put together like a RR horn and has the same two half bracket even. You may have a old Jeep horn there.