Signs of an Infestation
BITES:
Some people develop itchy welts, but others have no reaction at all. Bites can occur on any bare skin exposed while sleeping.

Remember that bites alone do not mean a bed bug infestation.
Confirmation requires finding and identifying the bugs themselves.
Live bugs or their eggs:
This photo shows adult bed bugs (dark, reddish brown) immature bed bugs (smaller, lighter colored bugs), and eggs (small white capsules). The black spots are blood that the bugs have excreted.

Photo from Bedbugsupply.com
Dark rusty or reddish spotting or staining:
These spots of dry digested blood may be found on sheets, mattresses, walls, and other areas

Photo by H.J. Harlan
Bed bug adults on a sheet showing typical fecal spots.

Bed bug stains near an air vent indicate that bed bugs may be travelling from room to room through the duct.