Yes, any offer that you come in on: free room, discounted room, E-mail, snail mail, those are "invitations".
Mostly, they don't really care, if the lines aren't that long. Check in wherever the line is the shortest.
Of course if your luck is like mine, the short line turns into twenty minutes while the one human ahead of you wants to argue about their room assignment or charges. This of course also applies at the grocery store (even worse--card denied, can't find checkbook in 10 gallon purse) or anywhere else. But I digress. Sorry. Rant over.
