The mysterious faces in downtown Madrid

While walking around Madrid one afternoon (perhaps the day we were searching for a supermarket on the way back to your place after lunch with Herm, Hannah?  I don't remember!), this apartment building caught my eye:

I think it was either an artistic or political display, but never found out what it was exactly.  Here's a close up of one side of the building:

I think we were near the city center, somewhere around Ópera or La Latina.  Has anyone seen this display in Madrid?  What is the statement being made?