droplifting

Droplifting is the opposite of shoplifting; it involves leaving a product or item in a shop, rather than taking one. It has been used by artists and musicians to promote their work for free, whilst some people use droplifting to make political or economic statements. (for example by altering shop's products and then returning them)

(droplifted) In addition to leaving merchandise in a store, droplifing may also involve coupons that the dropee does not need or want, discreetly left near the item affected by the coupon. It is extremely bad form to leave expired coupons but it's OK to leave coupons that expire the date they are droplifted. This form of droplifting is generally a female activity but not exclusively so.
A very polite and appreciated practice common in the Upper South i.e. southern Ohio and Indiana, West Virginia and Kentucky. It's more commonly done at stores that offer double coupon redemption such as Kroger and Meijer than stores that don't such as Walmart.
When a store has a super-double coupons redemption day or week, it is even more practiced.