From time to time there are cases when I would really like someone else to blow their nose, whether it be because they're constantly sniffling, or that I can see snot in their nose. Neither of those are nice things, so I really want them to blow their nose.

Is there any way of hinting at them to blow their nose? Or a certain way I could use to ask them to blow it?

This situation usually occurring around other friends/people too, so I don't want to say/do something that would place them in an awkward situation around other people.