Some rationale:
  • the lowercase b followed by uppercase B gives the idea of big and small
  • the small o looks a bit like a degree symbol, which feels sciency. It also contributes to the idea of small to big: o is smallest, b a bit larger, and B actually big
  • keep the same clear on black feeling as the default CSS output
  • yellow, green and blue are the colors of Brazil, where Ciro Santilli was born!
It might be cool if we were able to come up with something that looks more like an actual book though instead of just using a boring lettermark.
Some other ideas follow.
A letter square with uppercase monospace font letters:
OUR
BIG
BOOK
.COM
Could make the OBB red and other letters white. But that does come a bit closer to our dreaded ÖBB name competitor.

Ancestors