Good idea.

What I didnt write here in first was:

My original Thoughts have been about "how can I show people not to kill me".
Then I have been thinking about looking like old and calm people, which could be more trustfull...

This is genius, and very true blooded DayZ

This is actually a great idea. Beards surely will enhance how a character looks like. It would be also great if hair can be grown for both men and women.

but don't be fooled. kos'ers will kos.

This is a great idea! Your idea is very similar to what I have been wanting the developers to implement for a while now: some kind of aesthetic, viewable player statistic, or other recognition that adds value to the life of a character. As others have mentioned, all the value of a character is in their gear which, if you know how to play the game well, you can get pretty decent gear in a short amount of time. I believe this is part of the reason there is so much killing on sight
If player don't attach much value to their characters lives, they don't mind getting in fights because they're more than willing to risk their characters lives, and probably feel less bad for killing other players. If there was some recognition that you could only get from keeping a specific character alive, it would add value to the character's lives. Even if it was just statistics stating that with a given character a player lived for x amount of hours, killed so many zombies, killed so many other players, survived so many injuries and whatever else, then it would give more meaning to their lives, especially if it was viewable by other players. For example, you could see other player's stats by clicking on their name when you bring up the list of players on a server, and you can whether players on a given server are likely to be hostile or not by comparing the amount of people they've killed to the amount of time spent alive