It looks like one of the different cursor symbols from Google Street View to me.
Not necessarily unusual for it to be down for maintenance in the quiet overnight period, although it would be convenient if it was "down for maintenance" while something was happening.
Good call. TFL map shows that the buses use the next street over to the west (Whitehall).
https:// tfl.gov.uk/maps/bus?intcmp=40401&lineId=24
Hmmm, one of the routes traveling along Whitehall is [24].