In the past year, I have noticed an interesting trend with some of the stores that I have shopped at with my fiance; when you first walk into the store, an employee will be at the door greeting customers and saying, "Hi, welcome in!" I have never heard this expression until this past year or two. Generally, I hear it in brand-name stores like Kendra Scott, Kate Spade, and Coach. I find myself wondering if this is proper grammar, and the etymology of this phrase as opposed to the traditional, "Welcome." Is the "in" added to provide direction or additional meaning along with the phrase? So far the only discussion I've seen that might provide a little insight is here, way back in 2007:
So is it proper, and where does it come from?