Don't give up. Most women are aware of their affect on men to some degree. I don't think she would have left that message if she wasn't sincerely interested. She could have easily just wrote "Good Luck" or something. So if you happen to stop by your old job again make sure you check her out. Maybe you can arrange a small lunch gathering with her and a couple of your former co-workers. Ask her to it personally and express how much you are looking forward to seeing her. At the luncheon you should be able to get a better idea of how much further you could take it. It would be a good place to ask her out on a formal date.