[gibb0n]

1) When you drop everything you are doing to mentor other developers

2) When you get asked by the business to do something you question what they are asking and the motivation, and then determine the best course of action based on their motivation rather than delivering the specific task they asked.

That's it really, it's nothing to do with your coding ability but more to do with your mentoring ability and problem solving skills. This is what is valuable to your colleagues and the business. Any answer related to coding ability is missing the point, it's important, but after a few years most people are the same programming level - it's just some people can help at the team or business level which is what makes you senior.