When a person receives the Holy Ghost in the soul, they are sealed by the Spirit unto the Rapture when the body is changed to glorified condition according to Ephesians 4: 30: And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption. You cannot lose the Holy Ghost once you have received It and been sealed by It, but you can grieve the Spirit.
The evidence of a person having received the Holy Ghost is straightforward enough to understand. Jesus taught us that when the Holy Ghost would come, It would be the Teacher of the Word (John 14: 26: But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.), so the Holy Ghost is God’s Spirit dwelling inside a born again believer and teaching His own Word to the believer.
The actual evidence of a person having received the Holy Ghost is that they are able to be taught the Word, they can receive the Word, and they believe the Word. This is a self-explanatory thing, because when the Word is presented to a born-again believer, the Holy Ghost within them will be in agreement with It. God is not offended by His own Word, so His Spirit inside a regenerate believer will respond with an “Amen” to Truth, and the Spirit of Truth (John 14: 16 – 17; John 15: 26; John 16: 13) will bring the mind and body into submission to the will of God.