Luke, as well as the apostles, interpreted speaking in tongues as a sign of receiving the Holy Spirit:

• Acts 8:16: “For as yet He (the Holy Spirit) had fallen upon none of them. They had only been baptized in the name of the Lord Jesus.” The people in Samaria received the Holy Spirit after the apostles prayed for them. There was visible evidence because Simon “saw” it happen (Acts 8:18).
• Acts 10:44-48: Peter knew Cornelius’ household had received the Holy Spirit because they spoke in tongues just as the apostles had on the day of Pentecost. Likewise, based on the experience of the apostles, we also know that a person today has received the Holy Spirit when he speaks in tongues.
• Acts 19:1-7: Paul asked the Ephesians, “Did you receive the Holy Spirit when you believed?” and the response was negative. Why did Paul have to ask such a question if there is no physical sign when a person receives the Holy Spirit, or if a person receives the Holy Spirit the moment he believes? After they were baptized in the name of the Lord Jesus, why didn’t Paul just tell them, “you have now received the Holy Spirit”? When the Holy Spirit came upon the believers, there was clear evidence of speaking in tongues (Acts 19:6). Just like on the Day of Pentecost, the evidence of receiving the Holy Spirit today is still the gift of speaking in tongues.