Selecting Geometric Shapes

One thing I find very interesting is the ability select different parts of the photo and just change those.  Here in this photo, I was able to select the street sign and then invert my selection to choose the area around it to change.  My goal below was to ensure the that sign kept its color and the background changed.  As an example, I started out with the following photo and decided that I'd like to have everything in the photo to be black and white and to keep the sign in brilliant color.

Here is the photo that I began with.

Here is the same photo with the addition of a curves layer to alter the contrast.

Here is another one using different curves.