By Dr Deepu

 The melting ice(cube) sign describes the resolution of. pulmonary haemorrhage following pulmonary embolism. 
When there is pulmonary haemorrhage without infarction following PE, the typical wedge-shaped, pleural-based opacification (Hamptons Hump) resolves within a week while preserving its typical shape. It is named due to its resemblance with a melting ice cube.

1. Webb WR, Higgins CB. Thoracic Imaging: Pulmonary and Cardiovascular Radiology, North American Edition. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. 

Suggested Reading
1. Chest X Ray Part 1- Normal Anatomy And ItsVariants