From AMS Glossary
A signature on infrared satellite imagery that depicts a warm, wedge-shaped region stretching from the upshear edge of a thunderstorm anvil, downshear along its long axis.
This so-called warm wake is surrounded by long, narrow regions of colder pixels along either side, forming an apparent V shape. The warmer pixels may be stratospheric cirrus "blow-off" from overshooting tops, meaning that they are higher than the mean anvil height, even though they are warmer. The signature typically forms on convective storms possessing extremely strong updrafts.