an elevator has a central portion for contacting the suspension traction device the central portion has at least one of a protrusion and a marking for detecting whether the suspension traction device is positioned correctly on the pulley a method for monitoring the elevator system utilizes a noise detector for detecting noise generated by contact between the suspension traction device and the protrusion and an optical detector for detecting when the marking is covered by the suspension traction device application_number US 201315038789 A description in the fig1 and 3 three different pulleys 1 1 u2032 and 1 u2033 are respectively shown the pulleys 1 1 u2032 and 1 u2033 share a common structure with a central portion 3 the central portion 3 contains two end walls 4 and 4 u2032 the pulleys 1 1 u2032 and 1 u2033 are preferably made of a plastic material every pulley 1 1 u2032 and 1 u2033 has a plurality of markings formed as protrusions 5 arranged on the inner side of the end walls 4 and 4 u2032 whereby for perspective reasons only the protrusions of the end wall 4 can be seen the protrusions are made of the same material of the pulley 1 1 u2032 and 1 u2033 respectively formed integrally with the end wall 4 and 4 u2032 and have the same substantially hemispherical shape and dimension but are arranged with a different pattern in fig4 a side view of a substantially hemispherically shaped protrusion i is schematically shown near a substantially cylindrically shaped protrusion ii and a substantially conically truncated shaped.