Srimad Bhagavadam 4.15.9-10
Lord Brahmā, the master of the entire universe, arrived there accompanied by all the demigods and their chiefs. Seeing the lines of Lord Viṣṇu’s palm on King Pṛthu’s right hand and impressions of lotus flowers on the soles of his feet, Lord Brahmā could understand that King Pṛthu was a partial representation of the Supreme Personality of Godhead. One whose palm bears the sign of a disc, as well as other such lines, should be considered a partial representation or incarnation of the Supreme Lord.
Purport
There is a system by which one can detect an incarnation of the Supreme Personality of Godhead. Nowadays it has become a cheap fashion to accept any rascal as an incarnation of God, but from this incident we can see that Lord Brahmā personally examined the hands and feet of King Pṛthu for specific signs. In their prophecies the learned sages and brāhmaṇas accepted Pṛthu Mahārāja as a plenary partial expansion of the Lord. During the presence of Lord Kṛṣṇa, however, a king declared himself Vāsudeva, and Lord Kṛṣṇa killed him. Before accepting someone as an incarnation of God, one should verify his identity according to the symptoms mentioned in the śāstras. Without these symptoms the pretender is subject to be killed by the authorities for pretending to be an incarnation of God.
