Some couples have special songs that they use at various times. They may sing it together on a walk, at the start of a meal or event, in the shower, or in the car. For the self-conscious, humming or whistling seem to be favorites. The songs usually have special significance and are frequently silly children’s songs, or traditional folk songs from the culture. A song that has special significance to the relationship, such as being present in the early days frequently or during a particularly memorable moment, is also common. In this case, hearing the song (rather than reproducing it yourselves) triggers the heart connection.
A digital variation is sending one another songs back and forth that would be enjoyed in some manner. This version can offer a sense of play and predictability (that it will happen). E-mail, texting a link to a song, Facebook, chat clients, etc.
Finally, a musical couple (both were musicians) would write one another a song once a year, and then sing at their anniversary. The songs were different every year, and they would work on it all year long, so that the verses had a bit of history as well as sentiment mixed together.