Crowds likely did a double-take this week as they streamed into Mobile World Congress, the largest mobile tech conference on the planet. And not because of the new gadgets. Activists took over the sidewalk in front of the MWC to (literally) illustrate the environmental impact of e-waste. As far as messages go, this one ain’t subtle. The 3D pavement art opens a chasm of e-waste under the feet of attendees.