Being marked can be from heaven or, in future, from the Beast. How does heaven mark a believer? Various ways, I find. Some receive tongues. I never really got marked like that. A mark seals a believer. Interpreting tongues marks a person, like we see in Daniel when believers were marked by ability from heaven to interpret a message, from a dream, or even writing on a wall by a heavenly finger. It is sometimes such that it would be very difficult to credibly fake it, and maybe verified by several people doing it with corroboration. So it is a seal of authenticity from the Holy Spirit. Another mark is by miracles. It is a way God commends a believer too, especially when accompanying a ministry of preaching or guiding. The miracle may also verify to the believer the acceptability to heaven of the faith of that believer, as well as marking them as a believer to others. Another is prophesying. It can be an accompanying mark together with tongues. Again, the prophesying is a seal of the Holy Spirit which marks the believer. It can come in response to the laying on of hands by someone designated to do this, such as elders. Powers is a Holy Spirit mark similar to miracles, but like Samson, a power is given to a believer beyond earthly power to accomplish some task or meet a need, such as cleansing, sanctifying. Again it marks the believer so that other believers can recognise their genuine faith. It manifests the Holy Spirit, so it is a seal too. A believer might be marked many times in various ways. It is naive to only recognise one kind of mark such as tongues, or to reject such a mark, but denominations in some cases enforce such a stance, and therefore introduce and persist blind spots. Knowing you have been marked can help build confidence to participate more fully in the body of Christ with assurance of not being an imposter to do so. It provides assurance of acceptance with God, and a sign of the will of God being done on earth as in heaven, a glimmer of His kingdom. It is a step in being born again. But still we need to progress under this blessing and continue in the teachings of our Lord Jesus Christ.