"Note of warning" is a document in The Sinking City.
It can be found in the base floor of Blackwood's Flooded Office on the body of a hanged innsmouther.
It is a note presumably written by a member of the KKK.
Content[]
"We have warned you, yet you still return. This is our final message - go back underwater, or die. Reed Heights is under our protection. The police won't help you. No one will."