It means that the topmost layers of the sidewalls are showing signs of age and wear. Not too desperate but worth keeping an eye on.
They may just be coming to the end of their useful life
That's what's puzzling me. Both hubby and I live and work near London and I work more and more from home, the car hardly gets used, it has 7000k from new (3 years) on the clock,
...usually happens with low mileage cars (where age affects the rubber before distance-travelled wears them out) and particularly if left out 24/7 where strong sunlight (where's that? I hear!) can affect the outer sidewalls.
Not moving for days (weeks?) on end doesn't help either - the same part of the wall just sits in a flexed and load-bearing state for the prolonged period.
yep cracking occurs when the car is left for long periods, the bit at the bottom is in the same position for weeks. Then you use it and there is a different bit at the bottom, eventually the whole tyre is cracked. Not usually a disaster really that's why it's an advisory.