Can muggles see the skull with serpent cloud Dark Mark produced by Death Eaters?
Goblet of Fire example -
Then he realised it was a colossal skull, comprised of what looked like emerald stars, with a serpent protruding from its mouth like a tongue. As they watched, it rose higher and higher, blazing in a haze of greenish smoke, etched against the black sky like a new constellation.
Also seen at the start of the Half-Blood Prince.
It seems this is certainly no ordinary cloud formation so should be visible and provoke reaction?
I know the Death Eaters don't care about breaking the Wizarding Law or alerting/scaring muggles, but I was wondering if they could see this formation?