homeless signs - process work

During the summer my bicycle seat was stolen while my bike was chained to the city issue bike rack ouside of my downtown Toronto appartment. Following this, out of frustration, I placed a paper sign on the bike that read "Some bad-guy took my seat". Unexpectedly I found that someone went out of their way to add their own statement to the sign. What was it about the sign that made someone stop and react to it?
    When school started again in September, I dedicated my 4th year thesis project to exploring this question, and to causeing another such reaction, on a larger scale.

Mark Daye