Siren or 'wheel whistle'. Stamped Eureka.
Two similar instruments are shown as finials to 19th century walking sticks in Cane Curiosa by C. Dike (Paris, Editions de l'Amateur, 1983), p.143; one modelled on a German patent of 1887, in the collection of the author, and another in the Esbola collection, Switzerland (ibid, p.369).