Good question. You can have up to 3 karma arrows, either positive or negative. The rest of your question can be found in the Braingle Points and Awards FAQ:
Karma is a reflection upon how well you act in the Braingle community. When you perform a positive action such as getting a teaser approved you will get a little positive karma . If you perform a negative action such as swearing in the chatrooms you will get a little negative karma . Every time you do something on Braingle it will be calculated into your karma value.
The icons adjacent to your name show everyone your accumulated karma value. This can help you find friendly and helpful friends.
Additionally, users with too much bad karma will have their account restricted so they can no longer harm our community.
The exact formula for calculating karma is not made public.