Brief Answer
The topic of the signs of the re-emergence is a complicated one and calls for a thorough investigation of all the related narrations. However, in brief, the signs fall under two categories. One group consists of those signs which will certainly occur, foreshadowing the re-emergence: the rebellion of Sufyani, the rebellion of Yamani, the burst of a heavenly cry, the murder of an innocent soul, the sinking of the army of Sufyani into the desert ground, the rebellion of Dajjal. The remaining signs are not certain and as such might not occur.
But from another perspective, the signs can be categorized into four groups:
1. The social signs: that is, to put it in a nutshell, those social phenomena whose upshot would be the downfall of the then perverted human civilization.
2. The religious and Ideological signs: which constitute the collapse and distortion of the Divine religion.
3. The Natural Signs: changes such as alterations in the constellations.
4. The individual and miraculous signs: such as the burst of a heavenly cry, and the murder of the Innocent Soul.