The later clear yellow swirl stems are Bakelite. See beefeater33's meerschaum above. I'm pretty sure the early Ambera stems are pressed amber. Some people disagree with me on this. But the Ambera stems chip, fracture, and break much more easily than contemporary Bakelite stems do. And Bakelite doesn't oxidize as bad as the Ambera does. I've bought more pipes with broken or split Ambera stems than ones that are intact. I've never bought a pipe with a broken Bakelite stem. And I've never broken one myself. Ambera stems aren't even similar to Bakelite.
I guess the bowl markings have been worn, buffed or sanded away. It is odd though. Those pipes can have a lot of different stamps. KB&B clover, Kaywoodie, Suntan Rock Ambera, 4-digit code, Aged Bruyere, Synchro - stem with the patent number on the bottom. It can get pretty busy.