M VEM J SUN (P) - The planets in order. I guess we now just drop the P.
That looks too close to
UM,WTF? FFS!
I put the punctuation inside the closing quote if the original had it and otherwise refuse to. To me, it is wrong if it is not part of the quotation.
As for the OP, in my 86 years, I have never seen R for Th or U for Su.
Never seen that. Some languages basically call them “first day” through “seventh day”. The random mix of ancient deities we use is not very intuitive. I presume your guys went with the second letter for Sunday, but if so couldn’t say why they didn’t do that for Thursday. Any system that works for you, you do you yada. But I use different abbreviations and care little for your freakish choices. 
My undergrad schedule used MUWHF. If there were abbreviations for Saturday and Sunday, I don’t recall them. I still use those abbreviations sometimes if I’m drawing up a calendar or something.
I also write 7 with a line through it, which I learned in first grade while living in Europe.
I just go with:
Y Y Y Y Y Y Y
I consider R for Thursdays, U for Sundays to possibly be the most useful thing I learned when I was in college.
I rarely used the caps lock key because I’ve pried it out of my keyboard.
1 2 3 4 5 6 7 is another favorite
We learned R for Thursday from my grade school days. U for Sunday never took off, I assume in part because there was less going on or scheduled on Sundays. Especially during my youth when places being closed on Sunday was the norm.
I have only seen R and only for high school schedules, though it may have perhaps shown its face in college but I wasn’t paying attention.
It makes sense when you see how many Europeans write the number 1. My wife follows the European style, and her 1s have a much more pronounced leading stroke–often the upstroke starts barely above the baseline. In other words, a European hand-written 1 looks suspiciously like a non-crossed 7 with a droopy top.
I was born in 1959, attended school in a suburb of Cleveland, and remember “R” being used on school schedules.
At Virginia Tech in the late 80s and early 90s (at least) the scheduling tool used M T W H F. And that’s something that’s been stuck in my head ever since.
So do I (born in 1959) – I was taught “two spaces after a period or colon, one space after a comma or semicolon.” And (I’m defying the insistence of a science teacher that a sentence should never start with “and” or “but”) I agree with xtenkfarpi that a period should go after the closing quote unless the period ends a quoted sentence.
It strikes me we’re ignoring the obvious solution: Rename the conflicting days of the week!
So, with the state the world is in, do we really need to honor a war god? Nope! I propose Harmonia instead, the goddess of Harmony and Concord. (And goddesses are sadly unrepresented anyway.)
And, really, all I know about Saturn as a god is that he ate his children. This we need to commemorate? Let’s go with Bacchus instead. Which of us doesn’t revel and indulge a bit when the weekend arrives?
Which would give us the straightforwardd M T W H F B S. I could get behind that.
Apparently the first Y was “Yes,” for “weather station.” Most Canadian airports had weather stations, so they got a “Y.”
Why Malton was YZ, I have no idea.
I’ve seen R for Thursday, although these days I more commonly see Th. For example, if a class meets on Tuesdays and Thursdays, it will be abbreviated as “TTh.”
U for Sunday is totally new to me. I don’t like it.
I’ve finally broken myself of the habit of putting two spaces after a period. Really, at this point, continuing to do so is just being stubborn. And if you’re ever writing for publication, as I occasionally do, it screams to the editor, “THIS GUY CANNOT FOLLOW INSTRUCTIONS!”
When I was in sixth grade, “E” was used as a failing mark to avoid the stigma of an “F”, and a few years later, the school system adopted “NC” (no credit) for a similar reason.
Yeah, that’s what we were taught in typing class back in the 1970s. But one space seems to have been the default for some time.
What I want to know is, why can’t MS Word just have a setting that automatically collapses the two spaces to one? Lots of commenting environments online do that for you, including this one. So why can’t Word do it?
There are actually conflicting stories of whether “YZ” was a weather station call sign or an old railroad station code. It may have been both. The “Yes” reference arose from those airports also installing navigation beacons, so “Y” indicated that there was also a weather station there. The story goes that if they didn’t, the character “W” was used instead (for “Without”). Those Ws were either eventually superseded or changed to “Y”, but (contrary to my earlier assertion that all Canadian IATA airport codes begin with “Y” except for a few oddball Zs) there actually are three remaining “W” airports in Canada, all extremely tiny: WNN – Wunnummin Lake, WPC – Pincher Creek, and WPL – Powell Lake.
It occurs to me that a possible explanation of the weird choice of letters in some Canadian airport codes like YYZ, YUL, or YXU may be related to the fact that weather stations, navigation beacons, and railroad stations all communicated via Morse code back in Ye Olden Dayes, and those letter pairs may have had some Morse-related advantages such as having distinct patterns that reduced the chance of a mistaken interpretation. That would be especially important when using 1930s style automatic direction finders, where you identified a nav beacon by the Morse code it was transmitting.