Today I entered the Debug world type for Minecraft to check out all the new blocks in 1.9. Oddly enough I found an interesting block I had never seen before even after experimenting with 1.9. They looked odd and had letters on them like this:
What are these lettered blocks, and can I attain them?
They were used to test end structures, S stands for Save, L stands for Load, C stands for Corner, D stands for Data, but you can't obtain them. However, you can place them in a world with cheats are enabled by using the command /setblock x y z structure_block. A good reason to use them is the fact that they emit 15 light (as bright as sun) and their toughness is very high.
You can see the Wiki Post here.
