People alert their customers of coupons a number of ways. Here's how I do it:
1. I have a special coupon for my instagram followers. So I only list that coupon on Instagram (in both the bio and actual picture).
2. I have free shipping on orders over $50. I have it in my shop announcement (I think I did put it there. . . ) and in the actual item descriptions. I also put this on Twitter and Facebook.
3. If I have any other coupons, I do put it out there on social media. You can also put coupons in your shop announcment.
4. I have a special "Thank You" coupon. You can have this go out automatically when someone buys from your shop.