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.)