We see that Simon in Samaria believed from Phillip's preaching and was baptized:
Simon himself believed and was baptized (Acts 8:3)
When the apostles Peter and John arrived to Samaria, Simon must've probably been among those who received the Holy Spirit:
Then Peter and John placed their hands on them, and they received the Holy Spirit (Acts 8:17)
The following verse states that
Simon saw that the Spirit was given at the laying on of the apostles’ hands (Acts 8:18)
and in the verse 19 he wanted to buy from the apostles the ability of passing the Holy Spirit to others through laying on of hands.
One can assume that the Holy Spirit here was manifested in and perceived by others through various miracles similar to the miracle of speaking in tongues performed on the Day of Pentecost. However, we see in the verse 13 that Simon had already seen miracles performed by Phillip and was greatly amazed by them - and that had taken place even prior to the apostles' arrival and receiving of the Holy Spirit through them:
Simon himself believed and was baptized. And he followed Philip everywhere, astonished by the great signs and miracles he saw (Acts 8:13)
and yet we are not told at that point that Simon was trying to buy the ability of performing those miracles from Phillip even though he was greatly astonished by them. It was only after the apostles' arrival and seeing the passing on of the Holy Spirit by them that Simon decided to make a purchase. And the purchase would have been not about miracles, but about the Holy Spirit.
From this I gather that the Holy Spirit was categorically different from the miracles and signs performed by Phillip. And it must have been way more precious and more desirable than simply miracles. Also, the Holy Spirit must've been very very obvious. In fact, if Simon was not among those who received the Holy Spirit from the apostles in Acts 8:17, then the Holy Spirit must've been very obvious even to those who didn't have it.
So how was the Holy Spirit being seen or perceived then? Does the original text give us any clue?