In pictish Druid circles the Crescent is supposed to symbolise a temple of the moon nearby, and a V rod is added for male or female adepts in the mysteries of the moon. The V-Rod being angled at 82 degrees and facing up or down dependant on if the priest is a man or woman. They tend to discredit later crescents into the christian era as being christian priests copying the symbol without understanding it completely when you point out discrepancies. I don't know how much of it I go along with, but it's an interesting theory, especially as you learn about more and more symbols, some of which are in the nature of the things you see in the drum design; namely, toppological features of sacred sites.