Why do dogs do this?

This has happened to me on a few different occasions and each time it seemed weird. I would be walking along and a dog would grab my hand in its mouth. Not hard, not really biting me. More like leading me. Like; this way, stupid. It’s happened enough different times with different dogs that it can’t be a one off. Every time the dog has been a stranger that I’ve never met before. It is a little disconcerting, as the dog could easily change its mind and really cause some damage. It also is kind of nice, like a privelege. Does anyone know anything about this?