They baptize the dead, they celebreate the mysteries in public, they apply the name Jerusalem to their town Pepouza which, so it is reported, is in Phrygia where Maximilla and Priscilla and Montanus himself are known to have spent a period of their vain and fruitless lives. Where both a mysterium cynicorum and an accursed impiety [excecranda impietas], involving an infant, is celebrated. They say, in fact, that at Easter [pascha] they mix the blood of an infant in their sacrifce [sacrifcium] and that they send it in this manner to their pernicious and counterfeit congregations [perniciosis etfalsis satellitibus]. (Philaster Haer. 49)
It is apparent from Tabernee's analysis of all the material related to this report that tattooing or marking the body with needles:
An important feature of the orthodox baptismal ritual was the 'signing' or 'sealing' of the candidate as a symbol that he or she had been marked out as belonging to God. In catholic circles this was done by making the sign of the cross with oil on the forehead of the newly baptized person (Trad. apost. 22). If 'tattooing' indeed is the true meaning behind the Montanist pricking with needles, it is possible that the Montanists form of signing left a permanent mark. [Polluted Sacraments p. 356]
While Tabernee brings forward scholars who connect this practice with pagan Phrygian rites, a more plausible source is actually rabbinic traditions about Jesus or his associate 'ben Stada' engraving the Tetragrammaton on their body parts as part of a ritual initiation. In other words, we may be standing at the gateway to the earliest practices of Christianity.