What does a "V" pattern indicate if found at an arson crime scene?

It is the tendency of fire to rise and spread so that it burns a wall or other vertical surface in a V pattern, with the point of the V located at the origin of the fire. Crackling and flaking on floors and walls are indicative of places of high heat.

Explanation:

The plume of hot fire gases is shaped like a "V", while the flame zone is shaped like an inverted "V". If the fire itself is very close to or in contact with the vertical surface, this may result in a pattern displaying the effects of both the hot gas plume and the flame zone.