This is probably an easier question, but what is the plural of McDonald’s?
i.e. We stopped at three McDonald’szssz during our trip. *
*Phonetic spelling
McDonaldses? 
Very good, authority, which is all I asked for. 
“McDonald’s restaurants”
I would think the plural of McDonald’s is McDonald’s, just as the plural of sheep is sheep, and the plural of deer is deer. Likewise, I would say the plural of Sears is Sears, not Searses.
“We stopped at three McDonald’s during our trip.”
Yes, I think these are both correct. The possessive in McDonald’s is a short way of saying “McDonald’s Restaurant.” It’s like saying, “I’m going to Bill’s” meaning “I’m going to Bill’s house.” So if Bill has more than one house, you can say “I’m going to Bill’s houses” or “I’m going to Bill’s,” though the later would be ambiguous.
But sheep and deer are irregular plurals, so I’m not sure they’re the same as McDonald’s.
You may be right in that it’s a somewhat different situation. “McDonald’s” can be short for both “McDonald’s restaurant” or “McDonald’s restaurants.” It is not really a true plural. I was trying to make the point that sometimes singular and plural are the same.
So have we all decided that multiple hamburgers owned by the corporation are:
McDonald’s’s hamburgers
???
McDonald’s hamburgers is correct.
I picked up the right glove and the left of glove of Jane.
/mangled Sedaris
Quoth the Economist’s style guide:
This, at least, is not quite entirely true. One can perfectly correctly refer to, for instance, “The bo’s’n’s pipes”, meaning the pipes used by the bo’s’n (short for “boatswain”, but nobody ever uses that) of a ship.
Yeah, but that’s maritime English, which is weird to start with…
Ditto Nordstrom, which everyone around here insists on calling “Nordstrom’s.”
Perhaps we should just go with the romantic language family’s style of making a noun possesive.
hamburger of McDonald’s
hamburger from McDonald’s
I think people usually use the latter anyway.
If you can use that construction, there is no logical reason you cannot use the construction “McDonald’s’s” or “McDonald’s’.”
Granted, style is not always logical.
Except that "bo’s’n’s isn’t making a possessive out of a possessive. The first two apostrophes have a completely different function, indicating missing letters rather than possession.
Remember that McDonald’s was in fact originally a restaurant owned by two brothers, before Ray Kroc got involved.
I suppose that at that time the name of the restaurant would have properly been McDonalds’.
Although the spelling of the restaurant name throws a monkey wrench into the whole thing. I rather like the conclusion that the Economist reaches in similar cases.
Just be glad it’s not a restaurant owned by two guys named Moses.
Moseses’’ Hambugers?
Because, quite simply, it’s freakin’ ugly and will cause the reader to stuble. Like you said, style in not always logical, neither are grammar or spelling.
I thought spinning heads and spewing soup indicated possession.