Looks like leaf with shit on it. What are you feeding her ?did you put something on her? Did you leave her out in the sun? What nutes are you giving her? If you want help there are people here that can help you, however we need info. lovelylisas LG
also list the strain and a pic of the bottom? This an old leaf? Do they all look like this? Can we have a picture of the full plant?
considering the leaf hasn't turned yellow yet it could be Phosphorus deficiency. Also check for gray mold or spores in the plant as it could be something fungal.