The visual interpretation is one angle, but the real weight comes from its narrative function as a turning point for Harry. Before that night, Voldemort was a story, a faded evil. Seeing it in the sky, that tangible, violent proof, it shatters any childhood illusion of safety. It's the moment the war stops being history and becomes his present.
I've always been fascinated by how it operates on two levels: for the Death Eaters, it's a gang tag, a boast, a way to claim territory and spread terror. For everyone else, it's a siren, a dreadful confirmation. It collapses the distance between the cozy, hidden wizarding world and the raw brutality trying to consume it. That symbol hanging over the Quidditch pitch makes the entire magical Britain feel suddenly, terrifyingly small.
For me, the most chilling part isn't the skull itself; it's the snake emerging from the mouth. It turns a generic mark of evil into something distinctly Voldemort's, personal and predatory. It's not just 'bad guys were here.' It's 'He is here, or his influence is, and it's alive.'