Basically what you do is do something outrageous / funny as a marketing stunt, and then you photograph or film what you did and use it for your online social media campaign.
Your goal essentially is to do smart advertising that is offline, and then use that to ultimately market yourself online.
So for example if I were to do a marketing stunt on the streets of downtown Toronto, and then other people filmed it / photographed it, and then shared what they saw on Facebook, Twitter, and other social media websites then I have just done two things:
#1. I probably just gained a bunch of new clients / customers who saw the marketing stunt in person.
#2. I just gained word of mouth advertising via social media.
It is a Win-Win as far as advertising goes. The billboard above is for Copenhagen architects, and frankly I have no problem giving them kudos for their smart marketing campaign.
Below is some more examples of smart advertising which also garners social media attention:
