Pottery & Porcelain Marks – Square, Rectangle, & Other Geometric Shapes: Marks of squares, rectangles, and other geometric shapes have been in use since the 19th century and are still in use today. Many of these marks have a modern look with the basic design of a single line forming the shape. Names of the pottery that makes the pieces often appear inside the shape. There is also a combination of two or more shapes as marks. For English Registry Mark, see "Marks – Identification Help" and click on the "English Registry Marks" section.