Thanks so much! On some of your questions: The signs were initially going to be readable, but I couldn't find a nice way to fit the text in the way I wanted. Readable signs would have made the signpost enemy a bit more surprising for sure.
You're right that they're fires, but they have no purpose. They're masked as walls and just play a 2 frame animation. As someone who hasn't played any Souls games, it didn't register to me that they might be seen as checkpoints. In a bigger world I think turning them into checkpoints would be a cool feature, but in its current form the game is a one-shot sorta thing.