Here are some Peltier pictures showing the seams. They could be called cutlines, but generally these are called seams. Again both seams. Note, I am using a gray t-shirt for the background material. A gray background helps not-so-smart cameras get colors balanced. And a smoother background helps the camera focus on the marble instead of background textures. (Since my camera is picking up the stitches clearly, it's possible I need a smoother background to help the marbles be more focused.)
Again, I took pictures of both seams. The top left marble was so busy that it almost looked like it had three seams, but that's a different subject. I finally found the second true seam, and got that photo.
The top left one is a National Line Rainbo, aka NLR, from around 1930 give or take a couple of years. The top right is called a Bloody Mary. The rest are showing typical Rainbo patterns. (Rainbos are later than National Line Rainbos, and span the mid-to-late 30's through the 1960's. (Not sure if they were still in production in the 70's.)