came across the real life example , how they did infact post warning of Unexploded bomb's during the Blitz
London Air Raids DANGER UNEXPLODED BOMB sign at cordoned-off area in front of St. Paul's Church where a 1-ton, 8-ft. long time bomb was embedded & removed by a crew of bomb removers. Location: London, United Kingdom Date taken: September 1941 Photographer: Hans Wild