Culture under the cardboard box

I'm sure this must have been done in some capacity already, but it feels like something I would like to start or develop in some form...

I was randomly humming an old metal track, and discussing it with a colleague; when I thought about the idea of trying to covertly get the song into the heads of other people in the agency. A kind of unknowing cultural experiment where people could end up humming a song they had never heard before in a genre they probably don't listen to.

How can we create Covert Culture?

That got me thinking about the other possibilities of inserting culture into places it doesn't naturally fit. Music is an easy form of this, nudging a song into people's memories. Yet you could also do this with art, or poetry, design or even philosophy. A way of encouraging the absorbtion and trial of wider cultures and ideas.

The closest fit I can think of is graffiti putting personal comment into random locations, but I'd like to see something with more of a cultural agenda than a political or personal one.

Maybe it's putting art postcards in copies of Twilight. Putting a USB stick of classical music on the bar at a rock gig. Putting a book on the seat of a bus.

There must be hundreds of ways to spread culture in a covert manner. I'd love to think of a way to bring this to life...