thanks TMsn for the details, appreciated.
Yup, its abrasion on the outside of the tire. Will look around for some black shoe goo, but truth be told, some stores are rather down on stock, so I'll take what I can get, especially if I end up doing the trip.
I'll take the tire off and really check the inside of the tire, there may be nothing on the inside, but may consider a boot more out of caution. I have read of boots over time possibly causing issues to tubes with rubbing, but we'll see when I take the tire off again.
Ive only had a few sidewall issues in my biking experience, and while I agree with you that the cord structures look good, given that these Supreme tires have such a thin flexible sidewall, I'm sure it would be wise to do the outer shoe-goo thing to cover it up a bit, and while Im at it, I'm keen to put a sticky on Parks boot, just because they seem to be great for staying in place.
Going from the other recommendations of Shoe-Goo being less sticky etc, I'll try to find some.
I figure a boot where not needed is likely to cause more problems than not using one. It may eventually rub a hole in the tube, but I guess that isn't the end of the world. I just don't see a reason to add one unless the casing is structurally damaged. But I guess that is a judgement call.