In essence, it’s the view that the Chair (sede) of St. Peter is vacant (Vacante), which is to say that the current occupant of the Holy See is not recognised due to the modernist heresy of the Church hierarchy post Vatican II.
In this situation sedevacantists, for lack of a valid pope, maintain that the office has been vacant since the last legitimate pope (sedevacantists often cite Pius XII’s pontificate which ended in 1958 as the last legitimate occupant of the Seat of St. Peter).
As I said in the last answer, if I were a catholic I would eschew the Papacy and remain a monarchist, so I may as well stay as a traditional Anglican.
The symbol appearing in Harry Potter and the Deathly Hallows isn’t J.K. Rowling’s invention.
Known as the Tricirculus Lineus, the symbol originally appeared in Ancient Egypt in 2230 B.C. as a fertility symbol, reflecting a phallic line within a yonic circle, surrounded by a triangle presumed to represent pubic hair.
From Egypt the symbol was adopted by the ancient Greeks as an emblem of the perverse and creative sexual practices of the Egyptians, who in mimicry of their gods would commit an unspeakable act called Jamaharon involving fake beards, lettuce and canopic jars of mummy innards. Thus in Greece the symbol was used only on the most infamous of brothels. Called the “Horga'hn,” open display of the symbol was considered both obscene and bold.
Needless to say, the orgiastic Romans appropriated the symbol and applied it to their own hedonistic acts. It was Caligula who first adopted the emblem as his flag, which he flew on his insane ventures to fight Poseidon, and over the throne from which he declared his horse a member of the senate and sold the senators wives as prostitutes to the highest bidders. So the symbol quickly became a mark of insanity and cruelty.
Christianity soon took over the region and the Vatican grew strong. But under the Chair of St. Peter laid a strange symbol. The Horga'hn. It had been carved there by Pope Alexander VI, who had in his time as pope committed insane acts of sexual malevolence to rival Caligula’s own. It’s believed he encountered the symbol himself while on a state visit to the pagan ruins of Rome and mistook it for a charm of good luck. He thus had the symbol branded into the backsides of all nuns who took their vows during his reign.
The resulting mass nun exodus lead to a new sect of Christianity called the Khlysty, who used the symbol as their own emblem. Believing that in order to be forgiven by Christ one must first sin, and sin a lot, the former nuns created a religion of non-stop sexual experimentation, wanton sadomasochistic mortification and cannibalism that persisted until the rise of the Soviet Union. Banned under the new regime, the Khlysty died with their last adherent, Rasputin himself. But the symbol went on.
Stalin believed the emblem to represent Mother Russia in its imperialist prime and erected great monuments in its form prior to WW2 across the country. But as the war came to an end and great poverty swept the nation, the statues became rallying points for the poor and starving, and thus the symbol came to mean misery, starvation and death.
It was from this miasma of horrors that the serial killer Andrei Chikatilo came to be. Eating many of his child victims, Chikatilo adopted the symbol from its recent status as a hobo sign and carved it into his forehead, later inspiring Charles Manson to do the same. Thus the symbol became synonymous with mass murder throughout the 1970s, associated with the Zodiac Killer, the Son of Sam, and fictional killer Alex from A Clockwork Orange, the movie poster for which features the symbol prominently.
And it was from this film that J.R. Rowling was inspired to write the Harry Potter series, as many parallels attest. Considered “The Clockwork Orange of the 90’s”, Harry Potter went on to exceptional fame and fortune, popularizing the symbol once again as associated with magic and immortality.
And if you think that’s bad you should hear who Petunia Dursley is named after.