This will likely be against local zoning laws in residential areas. Usually they have very specific rules about what can and cannot be displayed on residential

This will likely be against local zoning laws in residential areas. Usually they have very specific rules about what can and cannot be displayed on residential property. Even if there are no rules on record for the municipality, nothing stops a motion being passed that would outlaw advertisements being sold on residential properties after the fact. Assuming you can get around the above, I would solve the cold start problem by first focusing on a single geographic market. Small, local businesses are more likely to purchase this type of alternative/non-traditional advertising - and they'll want to be able to market in their specific towns. I would also make sure that you provide some sort of science in terms of how the advertisements are targeted. Agencies will look for that. For example, an agency ad trafficker is going to want to market in neighborhoods with mean household incomes in line with their target audience.