I've worn thick disposable diapers in public without anyone saying anything. I doubt they noticed anyway but if they did nothing was said.
But if you do want to hide the diaper you can wear boxers or regular underwear over the diaper to keep the waistband of the disposable diaper from showing.
If someone does see a waistband of diaper they won't think it's a diaper right away. Unless it's an adult baby diaper with prints then they might realize it's a diaper poking out of your pants.
Most people aren't staring at other peoples butts anyway to notice.