1. Wetness (feel/sight) - not a sure thing, but an indication.
2. Odor (smell): It's in my clothes, usually. I always do a smell check prior to leaving the house and throughout the day.
3. Wipe your underarms and taste your own sweat. It will have an onion/b.o. aftertaste. It sounds gross, but it helps me know. (taste)
4. Like Miesry91: Lift your underarms in public and see how many people MOVE away/cough/rub their noses/clear their throats/stare in disgust
5. Generally: Lots of reactions from folks, but I don't rely on this. Some people know you from previous encounters and simply make a fuss over little stuff, it's best to go around people who DO NOT KNOW YOU.
I was reading deodorant reviews and I think it's a bit funny how self conscious people are about having any Body Odor . I read one review from a woman who was upset so about a certain deodorant not working. She called her *one time* experience with foul odor "traumatic" - I had a laugh a bit. People are very sensitive about these things.
That makes me think they can OVERREACT sometimes when they smell someone who has any odor. Nevertheless, as I have said before other people that I know with Body Odor don't seem to experience the same responses as I get.