I can't say for absolute sure what others notice or don't notice, but I tend to notice trends in interactions between individuals. Good or negative. I can almost always see what is coming usually, for that reason. An example is, if one of my friends gets involved with a guy, even if things seem absolutely perfect, I can sort of sniff them out, so to speak. I can tell almost immediately if the guy is just going to end up being a douche and break their hearts. And it usually does happen, but I never say I told you so because that is just awful. It can be really hard for me not to say "this guy is not as great for you as you think he is, you are going to get really hurt". But I keep my mouth shut, because it is up to everyone to make their own mistakes an learn their own lessons in life.
Another example is habitual behaviors in others...and if it is something that irritates me and the person keeps doing it constantly, while I hate to hurt feelings over it, I do tend to bring it up. Sometimes I can be too harsh tongued when I do and that is why I don't really like doing it. But I'm starting to realize that it is not beneficial to relationships to leave annoyances unsaid. If I brood on negative feelings instead of trying to resolve them, it just ruins things and causes me a LOT of stress, and I know this, so I usually always try to communicate and hash it out. This direct approach isn't always appreciated by other people though.