Calculating reactive power (Q) sign
CIVIL stands for (amongst other things) Capacitor, I leads V and V leads I in an Inductor (L)

So, given that the displacement between voltage and current can only be 90 degrees max for a reactive load, look to see if the current rises through zero before the voltage waveform. If it is then it's a capacitive load. It's easier doing this than looking for peaks. Clearly you need to know the AC frequency and you need to be sampling at least 5 or 6 samples per cycle to accurately determine C or L type load.