Hi charles, In most cases it is appropriate to ask an employee(or even better, a manaer) if they have any policies in place preventing you from vaping in Their establishment. Most places are more receptive to you approaching them before you take it upon yourself to just wander around their establishment blowing huge plumes of vapor ..... If you ask somone, show them your equipment then possibly demonstrate it to them they usually do allow vaping if it doesn't cause a ruckus with their other customers.
Keep in mind that you are in their place of bussiness, if you ask they normally allow it and will continue to extend this permission in the future to you and others who vape. If you are caught vaping without permission they normally (defensively) forbid it and will also do the same for others who undertake vaping in their establishment in the future......
I have not once been asked to not vape had I asked to be allowed to do so. I have been asked to vape in a less conspicuous place, and I have been approached as I was vaping and asked to tone it down because of a customers objection to it. I have been approached (in sears) by security and confronted for vaping in public but not once have I ever been asked to leave due to vaping .....
There is always a chance you will not be granted permission, in these instances it is better to comply with the request. And stealth vape if you must do so.....