Well I started having an obvious to others if I showed them bump at about 17 weeks (I could see one at 13weeks)
17+ weeks 
However it was easy to hide at work until I was about 24 weeks!
24+ weeks
I'm hoping to hide this one until at least 12weeks at work, I really don't want to be telling people until I'm out of my danger period. There are no signs yet, but I'm not quite 6weeks yet!