Is Nationalism a crime?

Most people would look at this image and see it as a typical scene on an average British high street. However the other day, I was sat on the bus which was stuck in traffic and I noticed several metal holders for flagpoles. I consider myself to be quite observant, and I wondered if anybody else noticed this, or cared if there were flagpoles or not.
I have been to America, and they have USA flags above every building, and that was New York, probably the most cosmopolitan city in the world, its diversity is great and makes New York be as special as it is, but at least the yanks are able to remind immigrants of exactly which country they are in.
That is not the only reason, I think that patriotism shows support for the army, the police and also gives the sense of a united belief between everyone.
Finally, just having the flags there would make people realize that they belong to one country, and they will feel a greater responsibility to show respect to the police and to the older people who might know that they live in one of the greatest countries in the world. Meanwhile it would make the town look vibrant and colourful, and the absence of flags just highlights how Brits are frightened to be patriotic in case in offends somebody. It doesn't matter how we have came to be like this, but I just feel that its a great shame.