This latter public gift is a manifestation of the Spirit that should normally be accompanied by the gift of interpretation, thus being equivalent to prophecy. Indeed, the public gift is not for everyone. The evidence is the fruit and the gifts. The primary fruit is love. Anyone who claims to be filled with the Spirit but doesn't have love is deceived.
Fruit validates gifts.
In the book of Acts, the most common initial sign that believers had received the Holy Spirit was speaking in tongues. This is a valuable gift to edify believers in their private devotions. The gift of tongues is a spontaneous utterance in a heavenly language, an overflow of the Holy Spirit which liberates the prayer life of the believer. It flows from the heart, not from the head. Another manifestation of being filled with the Spirit is prophesying.