Washed the car about a week ago. Roof was clean.
The car has been in my garage and NOT used for the past week, and the top has been down.

I just put the roof up, and noticed some dirt spots along a front crease . These came out of nowhere.
Is this a sign of an underlying issue, or do I need to clean wherever the tops sits when down?

 

just noticed the same right behind my head. don't keep the top down but I do lower it every chance I can. must be others out there. how do we stopthis and how do we clean it?

 

Given the current eastern seaboard heat and humidity those spots could be traces of mold, not dirt. When my wife's XK8 ragtop has shown signs of exterior mold during previous hot and humid summers, I've used the corner of an old cotton diaper soaked in medicinal alcohol to remove the mold spots. Just rub gently until the mold eventually disappears. No damage done to the top itself as long as you don't scrub too hard. Take your time with gentle swipes and just let the alcohol do the work for you....