When I ride I typically have a smile on my face since I'm having fun. I'll wave/signal or say hi to many of the people I encounter, especially if it's a nice day out or if I'm out in an area where the riders / people are more sparse. My signaling typically amounts to a smile and either a head nod or lifting a finger or two off the hood closest to the person. It's hit or miss whether I get a response. The "hardcore" roadies who seem to think they cannot show any enjoyment at all in riding rarely respond, but I could care less. There is also a certain group of roadies who are like me in that we can push ourselves, bust our asses, and still be happy about it. Those riders usually respond in turn and many of them will initiate the interaction themselves.

Do I need people to smile or wave at me when riding? Nope. But it's nice and honestly makes me happier when they do.