[Heaven's Tear] Sign of Twilight

Okay, so one day I found 3 Sign of Twilight on the ground. I don't know what they are or how much they are worth but they seemed a bit important/valuable so I saved them. However, I'm in need of safe/bank space so I'd like to sell them. I have no idea how much they are worth and I haven't been able to get an answer in-game. They seem too valuable to vendor for a hundred coins or whatever. I looked around the forums and wasn't sure where else to ask this. So. How much is each worth?

[Edit] I forgot to mention I saw them in someone's shop for 200k...sounds very crazy to me but I'd rather not chance throwing something out for 100c when it's worth much more.