Brats already answered it above this post of yours:

In other words, you don't know when you receive negative or positive Karma. So always err on the side of being nice, respectful, and polite, because you never know when you're going to be on the receiving end of some negative Karma.

Then wats the point of having it? We dnt knw who has bad karma. And wat yellow sign or label u talkin bout

If a user has severely negative Karma, a yellow warning sign will appear on their profile to warn others that that particular user is problematic. Here's an example:

http://dating.mobi/Poolhustler69

Yes you do when someone has enough bad karma it shows up on their profile in a big yellow sign. If you nice and curtious to people dont worry about it. It was for the serious harrassers to warn others of that person. So people didnt have to talk to them if they had harrassed alot of people.

@Andres: would u consider telling other users if a certian user has a high good karma rating? sort of like the oppisite of ur bad karma warning.

Ok thx for clearing tht up for me

I thought about this at the beginning, but the potential issue I see is that it would create an incentive for people to message others just to tell them to give each other positive Karma so that they both get the positive Karma award. I wouldn't discard it completely, but remember that Karma System was introduced to expose the serial harassers, and it's doing a very good job of that, so I would prefer to take a "wait and see" approach before changing the dynamic of the Karma System.