The penalty for counterfeiting and forgery of banknotes (imprisonment at least two years) appeared to the upper correct corner on the reverse of all 3rd collection banknotes. Note This is actually the put up-1970 variant, featuring "Freiheitsstrafe" as opposed to "Zuchthaus". Typical security features at enough time had been guilloches, https://petero753wkw7.celticwiki.com/user