There are a few Witches out there who wear their practice on them, necklaces, rings, clothes etc. Then there are others who dress like a Hippie and practice witchcraft. And then there are a few of us who don't wear our practice outwards, some people claim its the look in the eyes, or the aura or whatever. Most of the time its cold calling, making a guess.
There is no definitive way to tell if another person is a Witch, those some people just have a knack for figuring out someone.
Words? Generally some will say things like 'Blessed be' 'merry meet' etc very stereotypical 'Wiccan' addressing (Which is not always true), as a few youtubers I have watched state that this is the way for Witches to interact with the world, which is not true.
Never assume someone is a witch, a few people you can tell easily, other times some people just like wearing pentacles on their persons etc. And some people you could never tell.