Surface indications of a sulfur cave

There should be something on the surface that indicates that there is a sulfur cave under it, similar to the azalea tree for the lush caves. It doesn't necessarily need to be a tree, but it could possibly be a flower (probably a new one?). It could also be a just some smoke coming out of a surface crack, or a small sulfur pool.  

Alternatively, and depending on what biomes the cave can generate, the land on top of the sulfur cave could be like an oasis. If they surrounding area is, for example, a desert of a savanna, then there should be a patch of land with very bright grass and flowers that can be spotted from afar.