Stain from a termite tube
The stain stays after wiping it away, you must use soap and water and scrub. I often hear from customers that they found a small hole with what looks like dirt and that is exactly what a termite tube looks like. See the picture, there is a hole with a termite tube or old remnants. The tube was wiped away and all you have now is the stain. After treatment we usually remove the tube and any leftover marks if possible plus in this case the customer is going to paint. This is critical to the sale of a home, if you don’t get rid of the evidence the next Termite Inspection will note this and require an additional treatment. I also suggest repainting the floor or the foundation to make the holes blend in better, not to hide but make it more pleasing to the sight.