Images and depiction of the Bed Bugs Markings.
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.
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.