"Have a nice stay"?!

I’m always puzzled when I hear a clerk wishing me to « have a nice stay ». After some years in California, it’s not the complete emptiness of this statement that still strikes me, but its true meaning.
At first, I thought that my foreignness was the reason why clerks kept wishing me to have a nice stay: indeed, my accent, my hesitations, my more-than-often-completely-at-a-loss face was enough for anybody to read as NOT AMERICAN. The most educated would recognize my accent for what it is, while others, because also of my not-so-French look (to my mother’s eternal despair: tu devrais faire un effort ma Cherie, les hommes preferent toujours les femmes elegantes!) would ponder whether my outdoorsy attire was indeed proof of my German origin or may be Russian? (they should know better: in the kingdom of clichés, Russian women are very elegant too)
So, I would thank the thoughtful clerk and try to have a nice stay. How long the pleasant stay was supposed to last, I don’t know.
But after two or three years and an improvement in my language abilities and day-today knowledge, I begun in fact to feel offended by this seemingly innocuous statement. “Have a nice stay” How could a clerk know that I was a legal alien and not a permanent resident? Was there any unconscious wish from his part of kicking me out of the country, me, the deceitful foreigner? Because, in California, when you are white and act pretty casually, look bored- a good technique to not look as a tourist- and, in my case, when you haven’t spoken yet, it is easy for people to mistake you for one of them, an American. I mean, a true American. That’s why, without making any special effort, I can easily receive a connivance stare from another white person lost in a sea of Latinos or Asian faces; sometimes, I try not to speak so as to nurture for a while that new bond, to make the other only white person at ease for the time of her purchases at Target; sometimes, I engage her in a mundane conversation because I’m in the mood for a bit of meanness: maybe she will feel betrayed and disappointed to discover that, indeed, she is the only white-American person in the queue.
To go back to my point, I couldn’t and still can’t understand why the clerk would still part from me with that “nice stay”. To add to my puzzlement, I discovered recently that some “true American” are also told to “have a nice stay”. Do clerks receive a special kind of training to make the difference between locals and, say, Floridians or Montanans? I know these people can have a different accent and weight also a bit more than the average customer at Whole Foods, Monterey, CA; but still, their skill at targeting the non-native is extraordinary. The other day, the lady who was in front of me in the queue and who didn’t speak received nonetheless a gratifying “Have a nice stay”. I listened carefully: the clerk said “stay”, not “day” as I used to think that except from me, the other customers received a “have a nice day” as a parting word. So the big question is still: why on earth do clerk wish us a nice stay? Are they all very religious people and in that case, the “stay” to which they refer, would it be our life on earth? Would they wish us to make good use of our finite existence, would they be part of a secret sect of clerks, the “philosopher clerks” whose goal on earth would be to rekindle our sense of self and to incite us to live a more meaningful existence? But one of their principles would be, as in any good religion, to only speak by charades and metaphors? Are the clerks the new bare feet prophets?

I haven’t been brave enough yet to ask any clerk if it was so. But I will. And I may try to have a nice stay. Really.