What is neon gravestone?

A symbol in the lore of Twenty One Pilots's new album Trench. It is a bit difficult to understand if you are not into the lore of their albums.
Basically a neon gravestone is a headstone made from lightbulbs at a ceremony by the nine bishops to celebrate one who has committed suicide while captive in the walls of Dema.

Much like the song Neon Gravestones it is a symbol of glorifying death.