Black soot or stain?

[Amy Capozziello]

We just got our first propert, a four unit multi-home in Connecticut. The tenant in an upstairs unit moved out after one year and left large black stains on the wall where she had furniture or wall hangings.  One definitely is soot-like and wipes off, the other is where the bed frame was located and does not scrub off. It does not appear to be in any other units. The house is 1903 and the gas boilers are 8 years old. The unit is on the second floor. 

Has anyone seen this?