Ever notice the way people use the phrase, "Have a nice day"? Or "Have a great week"? Or "Enjoy your vacation"?
These are all essentially wishes, secular prayers. There is no expense involved in saying these things to anyone other than the cheap breath we expend while saying them. This is definitely not paradigmatic expensive signaling explored by Zahavi.
Therefore, we might as well wish BIG. Shouldn't we say, "Have a nice year"? Or even, "Have a nice lifetime"? Or I hope you live a good life for 1,000 more years"? Or, I hope that you and everyone you know, and everyone you don't know, and people who aren't even born yet, have ecstatic lives"? Or "I hope you and all present and future sentient life in the multi-verse enjoy your lives"? Or "If there is an afterlife, I hope that all of those sentient dead people in heaven and hell, and those formerly in limbo until that was abolished by the Pope, have great lives/afterlives"?
There is actually more going on than vapid wish-making. Notice that the length of time chosen by those who utter "Have a nice [choose a period of time] correlates with the next time that that person will communicate with you. A good friend might say, "Good luck with that project next week," knowing that you will communicate to each other in a matter of weeks. What if you only see someone sporadically? Then you might say, "Have a great summer." What if you might never see that person again? Then you might say,"Good luck with your new job" or "Good luck with that new diet."
Regarding those who actually know you, then, "Have a nice day" or "Enjoy your weekend" often signal social or emotional closeness.
This is not the case with the checkout person at a big box store, who hands you your bags of purchases and utters the phrase required by her oppressive corporation: "Have a nice day." I hate that these folks are forced to work like automatons, to the extent that they are made to utter canned phrases to customers. I like to break through that script, asking how their day is going, or whether they are working a long shift. If they are reciprocating, I "wish" them that they will enjoy the remainder of their evening. At least some phrase to break through the chatter we so often encounter, and make some semblance of a connection, looking them in the eyes and meaning it, when I tell them "Thank you." But never, "Enjoy the remainder of your life, as the time-treadmill of oblivion moves you inexorably toward your demise." That, of course, is a different topic.