Hey there. I don't have much experience with alto pieces, but have recently acquired a white Brilhart Tonalin Personaline piece. It has a 5 digit serial number on one side, and on the other side reads "S4", BUT it's almost as if it's stamped upside down. I can look at the mouthpiece pointed with the tip UP and read the 5 digit number, but the "S4" is printed upside down in relation. What does the "S" mean? I've also only seen Brilharts with the facing number on the front side under the label. Thanks in advance!