If it is not a mistake, it could have been a copy of what you find in a real M*A*S*H. I often wondered why they would have a Chinese sign with the characters for telephone switched around like that. The correct order is 電話, written left to right, right to left, or descending if it was vertical like in the photo. They do show this set dressing over and over again, that's why it stuck with me. Having translated a few documents recently, it's hard for me to ignore. As is, it could have a different meaning altogether.