51. How does a person know whether he/she has been baptized with the Holy Ghost?

The common sign given in the Bible by which persons were identified as having received the gift is speaking in tongues as the Spirit gave utterance.

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

– Acts 10:45
45. And they of the circumcision 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.
46. For they heard them speak with tongues, and magnify God. Then answered Peter,
47. Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?

– Acts 19:6
6. And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied.