Based on the information provided, the promotion method subway is using is sales promotion.
It is a marketing tool that involves letting know potential customers about a product that a company wants to sell.
Most common methods include:
This involves promoting or advertising products through sales, which means customers are offered special discounts or lower prices. This is the method used by the subway because the sub of the day is a sales.
Learn more about sales in: https://brainly.com/question/15375944