How do I show a promo code to customers?

Many Rover sitters have business cards with their promo code on it, you can buy them in the Rover store or you can use a service like Vistaprint who has a large selection of cards much more cost-effective and quicker delivery.

Since you are asking you may have found out that trying to text your code to a client gets blocked by the platform. If this is the case you can always take a picture of your code and send that via text; pretty sure that works.