Observant Pittsburghers have noticed a puzzling phenomenon: several numbered protractors have been appearing on city streets. They look like this:
A blogger named Eric has compiled over 60 protractor "findings".
People in cars (some might call them cagers) don't notice much, what with their cellphones, radios, air conditioning, and 3000 pounds of metal surrounding them, but bicyclists notice a lot of things when they're moving on the street. This is a Bike-PGH discussion of the protractor puzzle; the comments are quite funny.
Today my friend K. found Protractor #230 on the switchback ramps connecting the Washington's Landing bridge to the North Side trail.