What image analysis techniques can I use to extract the traffic signs from an image such as the one below?

![Exterior shot of a metropolitan roadside](https://i.stack.imgur.com/WGFUv.png)

Edit:

After Anisotropic diffusion: The background that i don't want gets cleared a little

![enter image description here](https://i.stack.imgur.com/wutQU.jpg)

After Dilation : 

![enter image description here](https://i.stack.imgur.com/bPbJ3.jpg)

Thresholding after Diffusion : Not able to figure out the best thresholding for this purpose

![enter image description here](https://i.stack.imgur.com/JhU6C.jpg)

However i am not able to figure out how to remove the background?

Edit : i just want these parts of my image 

![enter image description here](https://i.stack.imgur.com/SKDPX.jpg)

Taking another input image :

![enter image description here](https://i.stack.imgur.com/xkPXm.png)

Applying median filtering and edge detection :

![enter image description here](https://i.stack.imgur.com/PzSml.jpg)

After Bottom hat filtering:

![enter image description here](https://i.stack.imgur.com/B59zs.jpg)

**How do i isolate the road signs please help?**