The Universal Sign of Receiving the Gift of the Holy Ghost

"And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance." - Acts 2:4  

Because there were religious Jews in Jerusalem for the Day of Pentecost from all over the world when the Holy Ghost was first poured out, they were witnesses to the fact that God had miraculously fulfilled His promise. (Joel 2:28) For they heard their own languages being spoken by Galilaeans that had just been filled with the Holy Ghost. 

From this point forward to today, tongues - as the Spirit gives the utterance - is the one universal sign that a person has been filled with God’s Spirit.  

(NOT to be confused with “SPIRITUAL GIFTS” which includes “divers kinds of tongues” as one of nine “spiritual gifts” used in MINISTERING to the CHURCH BODY - 1 Corinthians 12:7). 

"While Peter yet spake these words, the Holy Ghost fell on all them which heard the word. And they of the circumcision [the Jews] which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost. For they heard them speak with tongues, and magnify God. Then answered Peter, Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we? And he commanded them to be baptized in the name of the Lord..." - Acts 10:44-48  

It was the sign of speaking in tongues that made it clear to the Jewish believers that God had also filled the Gentiles with the Holy Ghost. Peter told them, 

"And as I began to speak, the Holy Ghost fell on them, as on us at the beginning. ... Forasmuch then as God gave them the like gift as he did unto us, who believed on the Lord Jesus Christ; what was I, that I could withstand God? When they heard these things, they held their peace, and glorified God, saying, Then hath God also to the Gentiles granted repentance unto life." - Acts 11:15, 17-18  

Paul, coming across some disciples, 

"He said unto them, Have ye received the Holy Ghost since ye believed? And they said unto him, We have not so much as heard whether there be any Holy Ghost. And he said unto them, Unto what then were ye baptized? And they said, Unto John's baptism. Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus. When they heard this, they were baptized in the name of the Lord Jesus. And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied." - Acts 19:2-6