A sign holder arrangement for the support of a sign from an overhead support. The detector maintains proper alignment of a sensor emitter and receiver with different sizes of tubing. Moreover, the proposed method allows use of the total signal gain as the feedback signal, which is more robust against polarization-related issues than the traditional method using signal powers at several different channels as the feedback signals. The support arm extends downwardly and a guide member is attached to the lower end of the support arm and engages the belt. The rotation shaft member has a through hole that passes through the rotation shaft member in a first direction orthogonal to a rotation axis direction.