no that's not just a stain its cloth that's beened charred and burned away
Treat it in the same way you would treat any other burn. Cover it with a clean dry non-absorbant dressing and change it regularly.
if you eat a cigarette you will die from poplolameowmeow illness. why would you try to eat a cigarette any way weirdow.
Baking soda sprinkled over soft leather is a good way to get cigarette smoke out of the leather. This may take a little time to remove all the scent. Also charcoal wrapped in brown paper next to the leather can be of some help in getting rid of odors.
Oil it.
The cigarette might have rolled two layers around the cigarette, to avoid it burn all the way, because of people falling asleep with their cigarette in their hand, burning to death. Or maybe because the temperature falling because you don't force oxygen through it!
The only way to keep cigarette smoke outside a house is to smoke outside away from any open doors or windows.
If You Burn/Destroy A Death Note In Any Way, The Owner And Everybody Else Who Has Touched It Will Die.
The same way you'd treat any other burn.
The best cleaner is the classic soap and water. This is a cheap and very effective way to remove any stain or substance from leather.
The best way to get the rust off of leather seats is to not let it get there in the first place but if that is not avoidable then you can use any kind of highly rated leather cleaning products such as armor all.
Buy a leather care product such a Mothers Leather Care.