The most often seen sign of bed bugs is bite marks, which make no mark on some people, but leave red, itchy spots on others. Other than noticing the symptoms of their bites, there are several signs that can tip you off to an infestation. Bed bug skins or their eggshells are a sign bed bugs are proliferating inside your home. Their feces leaves dark spots on bedding or anywhere else they have been active. A common sign of bed bugs is a group of blood stains on your sheets or bedding, which means bed bugs have been feeding on you at night!