This could be accomplished by having a small hole in the middle, maybe 4 to 6 inches across, with a circular plate covering that, sectioned in the middle to slide apart like an opening mouth.

Underneath would be a screen to stop people from dropping things in, and a sensor to keep it from closing if someone were to put fingers in there.

The good part. Affixed below the screen is a potpourri type bowl, filled with the same or a scented oil. Randomly the "mouth" would open and emit a loud braaaap caused by a sound device powered by a battery, powered by a windup handle affixed to the nearest lightpole which local denizens would spin up of their own goodwill.

At the same time, a fan would operate sending wonderful smells of lilac or roses wafting through the air bringing some congeniality to a rushed and harried city.

These could be sponsered in part by local business that would use them as advertising for food shops. Rented out, they would emit odors 2 blocks away from a particular place to enhance ones desire for a certain item.

Buuuurrraaappppp (custard filled eclair scent)

"Did you smell that?"

"Look! Up ahead!"

[edit] Ooohhhh, forgot to add the best part...

once a year, right before a spring rain, the bmc's (burping manhole covers) could be retrofitted with soap bubble dispensers to fill a city with millions of bubbles.