Is this a signal?

Well I've only worked in the corporate retail world, I don't know if this is a little mom and pop store but overall, giving people discounts out of the kindness of their hearts wouldn't fly very well with their managers, especially if they're at the bottom of the sale totem pole. It sounds like it was on sale or damaged or the last one or a multitude of other reasons, random 50% discounts don't just happen out of the blue.

I'd say, if you really feel that she's interested and not just being nice, say hey I was wondering if you would like to grab some coffee whenever you're free, leave your number and leave. See if she calls you and if she doesn't then no harm done. As long as when you go back and shop there and you act like it isn't wierd, then she shouldn't either. Still be friendly but without any expectations.

Don't hang around trying to catch an open opportunity to talk to her, it's just awkward for both parties and possibly stalker-y.

Jam it back in, in the dark.