On the other hand unsigned types are a huge pain if you want to iterate through an array backwards because you have to use subtraction. A lot of people end up with something like this:

  unsigned int i = strlen(s) - 1;
  for (; i >= 0; --i) { // BUGBUG
      if (s[i] == '.') {
          break;
      }
  }

(Yes, you can make it work, but it is very error-prone when people try).