I've never pooped a diaper in public except for when I was a baby or toddler.
But I will say that whenever I've been in line at the grocery store behind toddlers or babies and they pooped in their diaper I could easily smell the poop.
So yes I would say that pooping in an adult diaper while in public would be noticeable.
I was also in front of an older guy who was clearly wearing adult diapers because I could see a bit of the diaper poking out the back of his pants.
He pooped the diaper and I could smell it but I didn't say anything to him because I'm sure he was embarrassed about it.