Even with AC current?

Without further context or qualification, 3V means 3V DC.

 

Even with AC current?

I suppose you should specify both voltage and phase!

 

Even with AC current?

Yes. A minus sign is a 180° phase difference, which is a BIG difference. The difference between the two hot lines in your home (assuming you have two hot wires) is 180°. Connect them directly together and you will have an idea how important that minus sign is.