There are a couple of ways that all believers can be sure that as children they are filled with His Holy Spirit.
Rom 8:15 "For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father."
Does your inner most being cry out "Abba, Father!" to your Lord in Heaven? Do you have a passion for God that sometimes you don't have words to express? That’s the Holy Spirit inside of you.
Rom 8:26 "Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered."
This doesn’t mean that your passion is always manifesting itself in tears and grand emotions! That may be part of it, but a continual, consistent passion for your Father in Heaven… that’s the mark.
There’s also another indicator:
Galatians 5:22-24 "(22) But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, (23) gentleness, self-control; against such things there is no law. (24) Now those who belong to Christ Jesus have crucified the flesh with its passions and desires."
Those who truly have the Holy Spirit dwelling inside of them will always be increasing in the fruit of the Spirit, and crucifying their flesh. It’s a law – just like gravity. Like a branch connected to an apple tree – as long as that branch is connected to the tree it will always produce apples! When the Holy Spirit fills a person, these fruits will always be grown.
Matthew 7:16-17 "(16) "You will know them by their fruits. Grapes are not gathered from thorn bushes nor figs from thistles, are they? (17) "So every good tree bears good fruit, but the bad tree bears bad fruit."
You can be confident that you have the Holy Spirit inside of you if your innermost being cries out to the Lord and longs for Him, and if you are growing in spiritual fruits, crucifying the flesh.