The posters themselves come in a range of different colors (check them out here) which all seem to bring a different sense of style to them ...... and then there's the parodies.
You can see some great looks that just use the posters in the image opposite, but there are other ways in which you can add a touch of this 'look' to a room.
The use of throw pillows can be very good and there are a number of these available as well.
I saw a display in a shop window a couple of weeks ago that used a poster of London on the wall with a leather armchair in front and slightly to the side of it with a Keep Calm cushion in it. The look was really cool and I visualized it being used with lots of bookshelves as well - your own private reading nook!
My middle niece has a turquoise Keep Calm canvas on her wall which she loves and when I came across comforter covers for beds as well I just knew that she would absolutely love to add that into her bedroom as well.
The trick is not to go overboard so instead of having a canvas or poster on the wall with this bedding I would either not have anything or just stick to a wall decal. You can get the canvas in a small size to prop up on a shelf or desk if you want to which will stop it being too over the top.
These are also available in a range of different colors (and even patterned backgrounds) to suit your decor.
The other thing I like about these cushions is that you don't have to stick with the usual saying, like the comforter that says Keep Calm it's Time for Bed there are cushions with a slightly different message too like this one -