The growth in active rewards membership is a positive indicator of customer loyalty and engagement. This increase is likely to result in higher frequency of visits and spending, as members of loyalty programs tend to spend more than non-members. The 13% year-over-year growth suggests that Starbucks is effectively attracting and retaining customers, which is crucial for sustained revenue growth. This news is likely to be viewed positively by investors and could lead to a short-term uptick in Starbucks' stock price.