Signage on Polish municipal police (Straż Miejska) cars uses both the standard form (Ż, on the door) and the variant with horizontal stroke (Ƶ, on the roof sign)
Its pronunciation is the same as that of the digraph⟨rz⟩, except that ⟨rz⟩ (unlike ⟨ż⟩) also undergoes devoicing when preceded by a voiceless obstruent. The difference in spelling comes from their historical pronunciations: ż originates from a palatalized/ɡ/ or /z/, while ⟨rz⟩ evolved from a palatalized ⟨r⟩.[1]
^Corbett, Greville; Comrie, Bernard (2003). The Slavonic Languages. Routledge. p. 690. ISBN978-1-136-86137-6. The spelling difference reflects the historical difference between a palatalization of /r/ (for rz) and of /g/ or /z/ (for ż).
^Edward Polański. "Reformy ortografii polskiej – wczoraj, dziś, jutro". Biuletyn Polskiego Towarzystwa Językoznawczego, vol. 60, p. 31. 2004. Warsaw: Energeia. ISSN0032-3802. (in Polish)