No prizes for guessing where this poster was spotted. It's advertising NetVibes, a service that "lets individuals assemble their favorite widgets, websites, blogs, email accounts, social networks, search engines, instant messengers, photos, videos, podcasts, and everything else they enjoy on the web - all in one place".
The most interesting aspect of this poster is that it contains a Data Matrix barcode which is a two-dimensional matrix barcode consisting of black and white square blocks, which can be read by enabled mobile phones and webcams. A Data Matrix barcode can store up to 2,335 alphanumeric characters. In the case of the poster above, when we decoded it on our iPhone it linked to the NetVibes website.