Last June, Arne, Michael Saladyga and myself hung the following banner on the front of AAVSO HQ :
The 40x3ft banner reads: "100 Years of Astronomy in Cambridge" in large letters with "Come in for a visit!" beneath it. It cost $350 and was paid for by the sales of our Centennial T-Shirts . HQ resides on a high traffic street in terms of both vehicles and pedestrians (thanks to a location right between two parks).
There were two main reasons we wanted to hang this banner. First, all previous AAVSO HQ's have been within half a mile of this location. Within the last 5 years or so there has been a shift in the immediate area demographics as local businesses and warehouses have been replaced with residential properties (mainly condominiums). There are lots of reasons for this, but the biggest may be the creation of the two large and modern parks and trails within a 1/4 mile of the location. Thus we thought it would be a good idea to take advantage of this location and let the community know what we do and who we are. This good will is important to having a healthy relationship with the neighbors. One is never sure when a neighbor's help will be needed. Secondly, HQ is literally up-the-street from the Harvard-Smithsonian Center for Astrophysics  (our very first HQ was set up there in 1918 ). So this is a form of guerilla marketing  in that it may help remind some of the CfA staff how close we are.
A sign on the front door describes what we do and welcomes the public for a tour between the hours of 10-3. The tour consists of watching the Citizen Sky video  on a projector screen in the annex, followed by a guided tour of the archives and artifacts. In addition to the banner, we hung a box of brochures and 10-Star Tutorials  on the front door for those interested but unable to do a tour. As of this writing (August 5, 2011) we've given out maybe 20 tutorials and 30 brochures through this box. Three families have taken tours.
Hanging of the banner was actually delayed by about a month due to the presense of a bird's nest that appeared right below it's intended location. We dared not hang the banner while a mother sat on her eggs. Even though the banner would not touch the nest, and actually provided some additional protection, we were worried that it would scare the mother away. So we hung it quickly one afternoon when the mother was away. Happily, chicks were hatched a couple of weeks later and everyone was happy.