Vaishnavas, when they talk about Brahman, usually refer to impersonal Brahman, brahmajyoti (rays of Brahman). Brahman according to them means God - Narayana, Rama or Krishna. Thus, the meaning of aham brahma asmi according to their philosophy is that I am a drop of Ocean of Consciousness., or I am soul, part of cosmic spirit, Parabrahma. Here, the term Parabrahma is introduced to avoid confusion. If Brahman can mean soul (though, Parabrahma is also the soul, but Supreme one - Paramatma), then Parabrahma should refer to God, Lord Vishnu.