A rotation indicator device comprises a body having a bore, whereby the body is adapted to be releasably mounted on a polygonal fastener or other multi-angled component in any selected position. At least part of the body which defines the bore is formed of a resilient material of suitable grip and flexibility characteristics, such as silicone rubber material, and the bore has an edge margin which is of a tapered profile in cross-section so that the body can be snugly mounted onto the fastener or other component without any relative rotation occurring between the device and the fastener or other component.