The only time I noticed an adult wearing a diaper is when I was behind them in the checkout line at Walmart and their shirt came up.
I saw the diaper which was a white plastic backed diaper.
However other than that I could not tell the guy was wearing an adult diaper by looking at his butt.
But with toddlers I can clearly see that they are wearing a diaper especially if they are wearing sweat pants.
The diaper will sag between their legs especially when they get full and then you'll notice a droopy diaper.
But it's more normal to notice a toddler or baby wearing a diaper and there's no need for parents to hide their babies or toddlers diaper in public.
Babies and toddlers do not care if someone sees their diaper as it's expected that they are wearing diapers anyway.
Also toddlers are not ashamed of having to wear diapers until they are potty trained because they know it as normal to wear the diaper.