It's payback time for mother bird

This advertisement from Hallmark appeals to reciprocity.  It asks moms to remember what their child has given them, and to act on this albeit subtle obligation.  A particularly interesting aspect of this add is that the main beneficiary of the ad, the child, isn't the one doing the advertising; the source of the message is Hallmark.

The classic study on reciprocity is by Regan (1971) demonstrating that a confederate who bought a coke (or didn't) for a participant in an experiment could then enlist them to buy more (or fewer) raffle tickets.

Regan (1971). The effects of favor and liking on compliance. Journal of Experimental Social Psychology, 7, 627-639.