Some pretty explicit photographs showing protesters carrying placards with dire warnings during a rally outside the Danish embassy in London on February 3, 2006 (protesting against the publications of cartoons in a Danish newspaper).

From the source website:

As many as 700 marchers participated in the February 3 rally, some chanting slogans and waving placards such as those shown in the photos threatening violence toward “those who insult Islam.”…

Heeding public calls for the prosecution of those responsible, Scotland Yard arrested five of the protesters in March 2006, charging the lot with suspicion of inciting racial hatred and four with suspicion of incitement to murder.

See the photographs here