Best way to empty a street is to drop a backpack in a rubbish bin (that's if you have any in the area). Guaranteed entire area will be evacuated.
Or play classical music, that really ticks the grommets off.
Unfortunately, mystery bags lying around in the street are invisible to Londoners: it only works on train platforms.
Equally sad is that my current hi-fi set doesn't have the requisite nutsack to compete with the locals blasting Beanie Man on their car stereos. In any case, I find that nothing clears a 10-mile radius around your gaff like David Tudor's composition "Pulsers" played at the appropriate volume.