When you can no longer pull your belly in :D thats how it was for me... when i was bloated i could pull in my stomach and then suddenly one day i couldnt do it anymore and it kept growing since that day :D
If you have a short torso, you can show earlier than twelve weeks. And my favorite first maternity clothes are ruched fitted tees, because they show your bump without looking like you're trying too hard.
If your pants are feeling snug could be showing already. I feel like im showing but i know its partly constipation and bloating or excess water not baby. Baby too small yet. 10weeks plus5. I did get told that after 12 weeks the belly just pops out so i think it depends on individual if people are staring
Your belly will go from big to small for a while depending on baby's position