Yes it is definitely a Nürnberg police OR helmet, probably Gemeindepolizei, made before 1918. Dating is only possible due to the cockade because this helmet type was worn from 1886 into the 1930s. Before 1918, towns with more than 5000 residents could select their own coat of arms if they wanted. After 1918 most other towns did the same, so there are numerous variations. Nürnberg units just kept their helmets without changes execpt for the cockades.