User blog comment:Bovell/New Modern Warfare 3 teaser trailers released!/@comment-74526-20110514144652/@comment-1518024-20110514150438

I think the OP is mentioning that in the Modern Warfare series, there are characters displaying the Union Jack, the flag of Britain. The newest in the series will obviously link to Britain. The most famous British city is London, hence why it was used.