For a classic German "Ausgang" sign try this
search engine link.
This is what UK regulations call Maintained Emergency Luminaires: They are always on and have to be. German regulations (I don't know if the situation in the UK is different in this regard) require them in places of assembly beyond the "exit" signs also for orientation lights, in particular on steps where these always-on lights can be one of the characteristics that distinguish a venue also with the auditorium unlit.
Such venues of course have also today a central power source for the safety lights. At a glance common voltages besides 24 V appear to be also 48, 60 and 216 V. From batteries of course, so always DC.