What are the signs that a person loves God and that God loves a person?
There is no objective criterion for this. The journey begins when man finds out that his sole concern is God. The Quran gives the criterion to discern between those who would be rewarded in the hereafter and those who would not be.
The first criterion pertains to one who would become deserving of punishment in the hereafter. The Quran says for such a person
He used to be happy with his own people. (84:13)
According to this criterion, those who earned and exhausted their resources on their family did not discover God! They could not think beyond their kith and kin.
The second criterion pertains to those who would be rewarded in the hereafter. For such individuals, the Quran says,
When we were among our families, we were full of fear of God’s displeasure. (52:26)
Such people were always actively thinking about their accountability towards God. In other words, despite being with their family, their sole concern was God.