Black, triangular object sighted during middle of day in large metro area.

I had just been to a job fair held inside a large hotel at 46th and Main.  It is situated on the top of a large hill in the center of the city. I walked out the back entrance and was enjoying the weather-clear blue skies and 70 degree warmth-when I noticed what I thought was a stunt kite due to the shape of the object.  I watched it for a few minutes wondering where the individual was who was flying the kite when it tipped over, and became a sliver of black, perpendicular to the ground.  It appeared to circle around the city but was very hard to follow because it was so thin.  I got to my car and tried to drive to where I had last seen it so I could get a view from underneath but I was never able to do so. When I first saw the object it was angling up into the sky.  After it reached a height far above the rooftops, it tipped over.  It was probably as big as my thumbnail with my arm extended.  I couldn't hear a sound and kept thinking that I should hear *something*.