Section 4 of the Public Order Act 1986 states that a person is guilty if they "distribute or display to another person any writing, sign or other visible representation which is threatening, abusive or insulting, with intent to cause that person to believe that immediate unlawful violence will be used against him or another, or to provoke the immediate use of unlawful violence by that person or another, or whereby that person is likely to believe that such violence will be used, or it is likely that such violence will be provoked." Therefore, a sign alone can constitute an offence if it meets these criteria. 

Key Point: Under the Public Order Act 1986, threatening, abusive, or insulting signs or visible representations can constitute an offence if they are intended to provoke immediate unlawful violence or cause fear of such violence, even without vocalisation.