Bed Bugs Blood Stains and Black Markings of the Feces.
The Black Markings caused by the Feces are the most prominent tell tale sign. The Red Spots caused by the crushing of a Bed Bug are less obvious.
The Blood Spots on a boxspring Blood Spots: These red to dark red spots are a result of a bed bug having been crushed by human movements in the bed. The shape of the blood spots is like that of a smudge. Sometimes, there could be somewhat of a streak too.
The Black dot like marks are Bed Bug feces. The bed bug feces remain like an extruding dot when the bed bugs excrete on a non absorbing surface like that of wood or plastic. However, when bed bugs excrete on mattress or box spring fabric, often this black liquid substance runs into the fibers of the fabric.
The Blood Spots on a boxspring and Black Feces Here is the same box-spring from another angle.
Please, do keep in mind that are many black marks of the bed bug feces for every one blood spot. However, the black marks of the bed bug excretions are a bit harder to find because of their size and location.