A sign needs advertisement consent from the council unless deemed consent covers it. A non-illuminated sign about your business, on the premises where you trade, is covered, within limits on where it goes and how big it is. Illuminated signs have different limits, so ask the council's planning team before you put one up.
Putting an A-board, table or other object on the pavement needs the council's permission under section 115E of the Highways Act 1980.