Here is a collage of the different markings found on these plastic CD 154 type insulators. CEECO-Communication Equipment & Engineering Corporation. CTC- closest I've come to is Centralized Traffic Controls Company. They worked with railroad signals etc. CTM- Continental Tool Mfg. Co. Railroad tools and signaling devices? L-W- L.W. Reinhold Plastics Co. And REN- Ren Plastics Co. If any body has any different information to add or correct I would love to hear it.