What exactly is a POS signature decline?

I didn’t buy anything and my card account is showing multiple consecutive pos signature decline fees so I’m wondering why exactly this is occurring and why are they taking money from my account when I didn’t even buy anything? The only thing I can think of is my card suddenly stopped working in the apple app store and when I re-entered my card info it kept saying my security code was invalid. I tried this three times with no success and as it turns out I have 3 POS signature decline fees. So what the heck is going on?

POS stands for “point of sale” and I would imagine that these strange messages are due in part to the iTunes store and your many attempts. Call the card company or go online and talk with a rep about your issues.

Pos Signature