The banner hung from a third-floor balcony, unfurling itself almost all the way down to the cobbles of the square. Barcelona no està en venda, it read, in large hand-painted letters: the city is not for sale. It wasn’t the first such slogan we’d seen in only an hour or so strolling around the narrow, winding streets of Barcelona’s beautiful old quarter last week, and naturally our curiosity was piqued. Something to do with gentrification, or developers maybe? Well, partly. But, disconcertingly, it turned out to have quite a lot to do with people like us, and possibly you too.