Assuming that the visual of the siren itself is incorrect - could you listen to these two clips for me (I must admit my tonal hearing isn't perfect since an operation - but these two clips sound v similar).
First is the siren from the film Silent Hill posted on youtube -
http://www.youtube.com/watch?v=IK13ntirEzE
The second is my recording of the St Malo test in France -
http://www.youtube.com/watch?v=QwG_WcMOlUA
Taking into account various film echo effects (such as the supposed close up of the siren - and the fact that this scene was filmed in a studio), what cemented my thought that there might be a link between the Silent Hill film and the French warning system is that the Director of the film Christophe Gans is French - so maybe he used a sound effect from his country.