Can God reveal to a person their destiny of either Paradise or Hell while they are still in this life, as a mark on the body, or are these merely satanic whisperings?

No one can be definitively assigned to Paradise or Hell except for those concerning whom a legal text has been revealed, for the specific destiny of creation is known only to Allah. There are signs that indicate a servant's righteousness or corruption, but these are not definitive; rather, they are glad tidings or warnings, and a person's ultimate state is entrusted to the Lord of the Worlds. Al-Tahawi said: "We hope that Allah will forgive the righteous among the believers and admit them to Paradise by His mercy, but we do not guarantee it for them, nor do we bear witness for them that they will enter Paradise. We seek forgiveness for their wrongdoers and fear for them, but we do not despair them." And 'Umar ibn al-Khattab, may Allah be pleased with him, said: "By Him besides Whom there is no god, if I possessed all the gold and silver on earth, I would sacrifice it to escape the horror of the Ascent (to the Hereafter)." There is no rest for the believer until meeting Allah, for the believer finds true rest only when they set their first foot in Paradise.