Which of the following is an example of a sign of termites?

Wings in window sills is a strong indicator of termite activity, specifically the presence of swarmers or alates. These are reproductive termites that leave the colony in search of a new nesting site when environmental conditions are conducive to mating. When they swarm, they often shed their wings, and finding these discarded wings in window sills or around the home signifies that an infestation may be nearby or that they have previously breached the premises.

In terms of the other options, while they might suggest various issues, they do not specifically point to termite presence. Leaves on the ground are common and can originate from various plants or trees, providing no direct evidence of termites. Cracked paint on walls can occur for many reasons, such as moisture issues, normal wear, or structural shifts, and is not a definitive sign of termite infestation. Wet soil around the foundation may indicate drainage problems or excessive watering rather than insect activity. Hence, the presence of wings in window sills is a specific and recognizable sign of termite infestation.