C is for...

Cast Iron
One of the interesting things about this project is paying more attention to the environment around me - I walk the dog along this road every morning and it's the first time I've noticed the pattern of 'C's on the manhole cover - I think they are hexagons with a piece removed. There's probably an idea for a typeface here if I had the time.

Update:
I've replaced the photo with a closer crop and in colour - works better with the previous entries. I've added an extra photo so you can see the pattern.