"I apologized, and went to grab the larger of our dressing cups (3oz), and brought it back to her. She had paid the bill in cash, and she told me she didn't need any change. I thanked her, wished her a good day, then went to close the tab (she had left me a 20% tip, which was INCREDIBLY generous of her).
"I was putting away more silverware when she came up to the counter and asked to see the check again. I obliged of course. She asked for a pen, which I provided, and watched as she flipped the check over and quickly scrawled something on the back of it. She slid the check and the salad dressing cup she had requested across the counter, smiled, winked at me, and said, 'This is if you ever need more.' She then picked up her back and walked out.
"I, being 16, innocent, and naive to everything ever, was totally confused by this. The busboy and dishwasher were snickering, and asked me what she slid me, probably knowing full well what was going on. I shrugged and brought the dressing container and the check into the kitchen with me. I looked at the check, and suddenly realized what had just happened.