I know MTWRF from Ohio State. I’d never seen Thursday abbreviated that way before that…
GT
Myself, I use a thorn for Þursday. Seems more historically correct. (You could also use Ð)
M T W Þ F
M T W Ð F
Going on 49 and I have never seen or heard of using alternate letters for Thursday or Sunday in my life. It’s really unnecessary because, almost by definition, you know what day is meant by the letter’s position in the list.
S M T W T F S.
I just have to add that I’m totally astonished by this.
I have seen this kind of layout, where space permits, M Tu W Th F Sa Su, and that makes some sense. But I’ve never seen M T W R F S S, and find the single letter substitution confusing.
In my understanding, Ð is NOT equivalent to Þ. Well, let me explain further. Being familiar with Icelandic, a language [and possibly the only language] that uses both those letters to indicate “th,” there is a significant distinction as to when each are used. Þ is used for strong “th” sounds, like the “th” in Thursday. Ð is used for the soft “th” sounds, like the “th” in father. Now, according to this chart on the International Phonetic Alphabet, you’ll notice that ð [the lowercase form of Ð] agrees with my explanation of its usage.
Anyway, to reply to the OP, R is fairly common as a one letter abbreviation for college schedules. My university used it, and that’s how I came to know it.
IPA usage is derived from Icelandic in this case, for which you are quite correct in every detail. In Old English, however, they are more or less interchangeable insofar as we can tell at this remove (cite: Roger Lass’s Old English: A Historical Linguistic Companion). Still, in deference to our Icelandic brethren, we can go with Þursday over Ðursday.
Actually, at my school we do not use ‘S’ for Saturday. We also use ‘U’ so your schedule will say M T W R F U instead. It makes sense to use a different letter at my university because you have some classes that meet on Monday, Wednesday and Friday and other classes that meet on Tuesday and Thursday. Using a ‘T’ for Tuesday and Thursday would have caused too much confusion when you can just change the letter.
What about Saturday and Sunday? Or should we write a little picture of a sun in?
M T W Þ F S ¤
Okay, I know you weren’t serious, but I like it. If I’m ever running a university, I’ll use this.
From Michigan, and I only remember seeing:
S M T W R F S
You don’t have to distinguish between Saturday and Sunday because you just put Sunday at the beginning and Saturday at the end.
edit: Okay, now I’m starting to doubt myself. Maybe it was S M T W Th F S. I have no idea anymore.
Yeah, that’s about right.
Of course if we spoke Portuguese we’d be sitting pretty: 2 3 4 5 6 S D (they use ordinal numbers for weekdays).
Dr Drake and nashiitashii, your clarification, please:
It was my impression that thorn was the symbol for unvoiced “th,” as in “thin,” while edh was the symbol for voiced "th,"as in “then” – no “strong” or “weak” about it – and that Old English and Early Middle English, like many languages of the day, was rather careless about precise spelling and would use the letters somewhat interchangeably, but with precision usage being as defined above.
In Old English, certain voiced and unvoiced consonants were distinguished by position, not spelling. So fisc was pronounced “fish” and heafod was pronounced “havod” (approximately). An Old English speaker wouldn’t have considered [f] and [v] separate letters, just two ways of saying the same thing. Same for [s] and [z], and the two varieties of the <th> sound. Between vowels, it got the voiced pronunciation (v, z, th-as-in-then) and initially the unvoiced (f, s, th-as-in-thick). This is why some dialects still say “house” as “howss” but “houses” as “houzez.”
Old English had two ways of spelling <th>: ð and þ. You’d think that they would have noticed that they had two letters for two sounds and matched accordingly, as the more clever Icelanders did, but they just didn’t. Instead, ð fell out of use, and then þ, and they used the less elegant <th> for both sounds. Meanwhile, the voiced / unvoiced distinction had become phonemic, which is why the whole notion seems incredibly counterintuitive.
So, for linguists and Icelanders, Þ is the hard (voiced) <th>, and Ð is the soft (unvoiced) <th>, but for the Anglo-Saxons, they were just two different ways of writing the same letter, which represented two different sounds depending on phonetic environment. (I checked David Crystal’s The English Language and Mitchell’s An Invitation to Old English for verification. Crystal has a pretty clear and accessible explanation.)
I’m not a linguist by profession, so if the real ones want to chime in and correct / explain better, please feel free!
The airline booking system we use designates Thursday with a Q and Saturday with a J, which intuitively, makes no sense. We tend to call these days “Qursday” (a single U should suffice here) and “Jaturday.”
Well, this is news to me. However, perhaps it is an improvement on the bar sign telling us when a band will be there. “Chixdigit WTF.”
At Kent State in the late 70’s it was MTWHFS…don’t think there were any classes on Sunday. I still use the H when I’m making a note of my schedule for the week on a Post-It that I will surely lose before I can enter it on my calendar.
I wholeheartedly approve of this strange new method of denoting the days of the week and I may start a petition to have it adopted into UK universities.
Of course, with our slightly different pronunciation we’d be calling it ‘Arseday’ 
I usually go with Z X ET B 4 V A, that way, there’s no confusion.
In an aviation weather METAR, smoke is expressed as FU (short for fumee, which is smoke in french).
From this site, the NOTAM contraction for smoke is SMK.
Well, except that in a class schedule, they’re not going to all be lined up like that.
So if you have a schedule something like this:
Chem 101 9am-10:40am MW
Chem 101 9am-12:30pm S
Chem 101 5:45pm-10:30pm R
and so on…
You know that the R refers to Thursday and not Tuesday.