Warren gets out of bed in the early hours for the first time and with a choice of 2 murder sites to check out he goes straight to see a piece of chalked writing in a doorway?
As soon as the police removed the piece of apron how could any of the locals (i.e. Jews) be expected to connect the writing with the Murders? It's hard to believe that there was ever a real chance of some kind of riot even IF the message was, in their eyes, linked to the murder (i.e. an accusation against the Jews). But if the cloth had been taken away a policeman guarding the message could have been given any kind of cover story for the public as why he was there ( for eg. 'I've been told to watch for suspicious behaviour, now move along.'). I recall Bruce Robinson saying something like 'if they could seal off Mitre Square, which has 3 exits, and stop anyone going in or out, surely it wouldn't have been beyond the Met to seal off a doorway in an east end backstreet?'