Final answer:
While all the options could relate to different aspects of customer engagement, Email or newsletter signups are a direct measure of consumers' interest and willingness to engage with the company's content.
Step-by-step explanation:
One way to measure success at the consideration stage is with customer engagement. Among the options provided, a good measurement of engagement is b. Email or newsletter signups. This metric indicates the interest level of customers in receiving more information about the company's offerings, and their willingness to stay informed about future updates and promotions.
Rewards program usage may also reflect engagement, as it suggests that customers are interacting with the company's loyalty initiatives. Return customers are another key indicator because they show an ongoing preference for the company's products or services. Lastly, while the number of sales is an ultimate business goal, it is more of an outcome of effective engagement rather than a direct measure of engagement itself.