Re: OOC
Technically, there would be a roll involved to detect the energy in the first place. It could be made untrained as well. However, assuming that you sense something without making the check is what is commonly reffered to as 'God Modding', and is frowned upon in most roleplaying games.
We didn't state a DC either, so we can assume that you don't sense it unless a GM specifically says you do... possibly.
Either way, even if you detected it, identifying it, or even suspecting that it's a clow card would require ranks in Knowledge (Clow), which nobody but a Cardcaptor or Li Warrior can have.