One Legged Wonder

There is also some messenger looking fellow who I often see pelting along whitechapel road with only one arm. I came up to him at the lights once and really wanted to shake his hand.. hmm maybee not.

Why not? Chances are that he would see it as a perfectly normal greeting. Try to watch out for signs from him that it makes him uncomfortable and if you don't see any, he probably doesn't see anything wrong with being touched in greeting in this way. It can often be the awkwardness of people who feel apprehensive about physical disabilities that is more inappropriate. A greeting can bridge a divide between us, there's a reason why such gestures exist, and they don't necessarily change just because someone has a visible physical disability. Disabled people are still people who understand life in much the same way that we all do.