All around me are things which are well designed. My TiVo, for instance, has three fast forward speeds. When going through a commercial break at 64x normal speed, I can still be assured that when I see my show come back I can hit the PLAY button and the TiVo jumps backward most times to just the right place where I intended to stop, instead of at the point where I actually hit the button. It's pretty obvious that a lot of thought and effort went into the design.
When we see an object we can often tell instantly about its design by how well it fits the function for which it was intended. For instance, look at a car.
Regardless of the particulars, you can tell it's a sophisticated piece of design. The intricate sleek shape, the way the doors fit nicely, the materials used all indicate the efforts of a team of skilled designers. But a machine doesn't have to be so complicated to show the level of thought that went into its design. Even something as simple as a hammer speaks volumes about the design. Different kinds of hammers are optimized for different tasks, and believe me, an extra inch in length or a few degrees of curvature in the claw of a hammer can make the difference between efficiency and frustration.
When we designed our deck I was surprised to learn about the level of thought that went into steps. The height, width, depth, and overhang all require thought. Or look at something like Stonehenge. Even though it is just a pile of rocks, nobody would mistake it for just a pile of rocks, because it clearly shows the intent of the designers.
But perhaps I'm being a little prejudiced in talking about human accomplishments. Even a bird's next is clearly distinguishable form a random pile of sticks.
Which is why it always boggles my mind that people can look at the following and claim that there's no evidence of any design or designer.