To me, I started showing a little belly around 12wks; although I was so crook for 10 weeks I literally went from having an inverted flat stomach to having a little belly.

At about 15wks people at work suddenly started commenting that I had 'popped'; my chest definately got bigger too around that time.

I like wearing clothes around my waist so I moved into maternity skirts and pants around 12/13wks to be more comfortable. Generally random people in the public have started noticing now around 18/19wks. (Unfortunately not enough to stop rude people from elbowing past)