What is the meaning of ‘in hoc signo vinces’?

What is the meaning of ‘In Hoc Signo Vinces’? Traditionally translated ‘in this sign thou shalt conquer’, this is a phrase in Latin which in turn originates from the Greek ‘en toutoi nika’ or ‘in this conquer’. 

The phrase is historically linked to Constantine the Great, the first Christian Emperor of the Roman Empire. Prior to the Battle of the Milvian Bridge, fought outside the walls of Rome in 312 AD, Constantine is said to have seen the image of the labarum (‘Chi Rho’ cross) representing Jesus Christ in light above the sun with the words in Greek ‘en toutoi nika’. Constantine, apparently unsure of the meaning of this event, went on to have a dream that night in which he was spoken to by Jesus who told him that he should use the sign of the cross against his enemies.

Constantine’s forces defeated his opponent at Milvian Bridge and he was to use the labarum standard from this point forwards in his campaign. 

Constantine’s rise to sole power continued after his victory at the Milvian Bridge, become sole ruler of the Empire, and to found the city of Constantinople on the site of the Greek settlement of Byzantium. His rule saw the Edict of Milan, which gave full tolerance to Christians in the Empire, and lead to the eventual victory of Christianity as the religion of the Romans.