Here are some things I consider friendly.
1. Smile when I pass you.
2. Say, "How's it going".
3. Wave in the parking lot.
4. Say hi to my kids.
5. In a meeting, nod like my contribution was valuable instead of checking your watch.
6. In a group, give and take in conversation. Or just listen without checking your BlackBerry.
If you want to actually talk, I'm up for it.
That's . . . pretty much it. I don't want any stalkers or creepers telling me my hair smells nice.