"German writing"

These chalky squiggles, frequently to be seen on rocks, pebbles, shells, seaweed  and all sorts of marine debris, in this case the funnel of a lobster pot (see extra), are the  homes of the keeled tubeworm Pomatoceras triqueter. 
When submerged the worms put out tentacles to catch plankton or other food particles in the water. When they die the tubes remain as if embossed upon the surfaces. 
Oyster fishers called  this "German writing" because the vermicular scribble resembled Gothic script and spoilt the appearance of the oyster shells. 

Natural calligraphy that must have preceded the written word by countless aeons.