SOON is a common caption in image macros that typically feature a creepy looking figure peering out of a dark enclosed space or a figure looking out from a a window or closed door. The caption implies that the figure is plotting some sort of devious scheme, intended for either the viewer or a person or object in the foreground.
One of the earliest known images utilizing a SOON caption featured an angry looking orange cat glaring at a small Chihuahua puppy. (Picture above)
"Soon"... The Part 2