Grim

A grim is an omen of death first mentioned in The Prisoner of Azkaban by proffessor Trelawney while Ron reads Harry's future through tea leaves.

They first meet Sirius at the Whomping willow and mistake him for the Grim.

The Grim's symbol in the tea leaves are a wonky cross and a sun. The cross trialling in suffering and the sun in happiness.