I guess it differs for everyone.
Your vascularity and striation will start to show from anything 9% and under if you ask me. 3 - 5% is only maintainable for a VERY short period of time. It is pretty dangerous and unhealthy. Males have 5 - 6% of essential bodyfat on their body, without that you are going to be doing detrimental things to your body.
For most, anything under 10% bodyfat is very visible abs.