Oh dear Og that’s terrible. Go fly away. [/even worse spinoff joke from the same concept]
The J has a bar across the top. That’s the way I was taught.
The 7 and the Z can have bars, but in the US they usually don’t.
I’ve taken to striking a horizontal line in the 7s again after realising my 7s and 1s are virtually indistinguishable (spelling?). My Gs look like 6s which I have to rectify. The thing is, spending so much time typing rather than writing has made my already horrid handwriting deteriorate into something akin to Linear B.
I first heard of the line through the 7 in 7th or 8th grade mathematics, when my teacher made the point that with my admittedly barely tolerable handwriting, it would help both him and me to follow my work. I use it now, to keep from confusing myself with my own writing.
Similarly, I put the line through the 0 as well. I don’t use a line for a Z, but if I ever had to use a lot of Zs I might start.
I cross Z when I’m doing math to distinguish it from 2. I don’t cross my 7s because they don’t look like anything else. I do put a bar on the top of capital J, probably because I put serifs on capital I to distinguish it from lowercase l and j is similar to i.
How odd. Perhaps your professor was thinking of this letter, which is in fact distinctly different than o.
My J’s sometimes have hats on them as well: Ĵ. 
(Ĵ is a different letter than J in Esperanto.)
I picked up the habit of writing my 7’s and Z’s with cross-strokes in university; in my scribbled writing, the Z’s do tend to look like 2’s. I have seen Europeans write 1’s with a second stroke at the top, similarly to that fancy wedding-invitation script, so it would make even more sense to write their 7’s with a cross-stroke.
Now, zeros with a cross-stroke are very confusing, because Ø (the letter O with a cross-stroke) is a letter in, I think, Norwegian. Or possibly Danish.
I put hats on my J’s sometimes. I always cross my z’s or they look just like my 2’s. I don’t hook my 7’s unless I am trying to be very precise, and I haven’t crossed my 7’s in years.
My mother wrote in the British way, having been taught in an Indian school that still had tons of Brit influence in it. So I picked a lot of this up from her.
I put a line on capitol J’s from time to time, based on whim.
I’ve never seen the Z with a line through it, but I have seen plenty of 7’s with a line (my father does it, for starters, and I doubt it’s due to a European influence, as he didn’t leave the United States until he was in college), even though I don’t do it myself (I don’t include the top dash on 1’s, so confusion is not a concern).
That’s weird that your wife thinks that’s weird. I always used a bar on top of my capital Js, and gradually picked up the habit of using a line through my z’s and 7’s.
For a while there, I used a diagonal through my zeroes as well in Algebra, but stopped since it took longer than I really liked to write it out.
Both
My hats have NOTHING to do with Esperanto. 
Yeah, it is European to write 1s with a little swoop leading up to the straight line, so that it is often necessary to put a line through the 7 to distinguish them. I write 1s as just a straight vertical line and sevens without the crossbar, which my students have learned to deal with but caused some confusion at first. I write the date on the whiteboard every morning and a few students pointed out to me that I had written the year as “2001”.
I can’t imagine leaving the top line off the J when writing. I would recognize it as a J without it, but it looks…incomplete. FWIW, I learned to write in California in the early 1980s.
I don’t put a bar at the top of J’s, but I do cross my Z’s, both upper and lower case, to avoid confusion with my 2’s. My father gets indignant at this, claiming that if I made my 2’s the “right way” (with a loop at the bottom), it wouldn’t be necessary to cross my Z’s. Yes, but then my 2’s would look dorky.
I don’t cross my 7’s, since my 1’s are just a vertical line. If I’m writing a line of mixed numbers and letters, like a software license key, then I put both bars on my I’s. I also put a slash through my zeroes unless it’s obvious that I’m writing a number. I don’t slash the zeroes in $1,000,000, but I would in H0HC92T00O. One of my math teachers in high school grumbled that a zero-with-a-slash is not a zero but the null set. Yeah, whatever. I need to distinguish zeros and O’s a lot more often than I need to use the concept of the null set.
[aside] Once I nearly strangled a co-worker who was confused about a software key and kept asking if a certain character was “the letter zero”. She was a dolt, though. [/aside]
I work with a person who makes 3’s so bad that, unless it is clearly a 7, I assume it’s a three.
Wrong, the number 7 in English is as shown. The line through the centre is a a poncy European invention to distinguish the number 1 which is as shown from the stupid number 1 which looks like a pup tent with a saggy left sheet.
J has a bar across the top, O doesn’t have a line through it and nor does 0 or Z
Have you guys learned nuffink?
I started using the slash through the 7 several years ago when I was waiting tables. A friend presented the check to a table for something like 78 dollars. The customer added a tip of 4 dollars and wrote out the total for 32 dollars. The friend pointed out the error and there was a nasty argument even though all the totals including the bottle of wine were on the check. In the end he signed the slip for the 78 dollars with no tip and walked out muttering. To this day I am almost possitive it was a scam because the friends 7s were really crisp and because you can’t get dinner four 4 with wine and desert at a midrange restaurant for 28 dollars. The little slash avoids the opportunity though.
I had a lot of people confuse my handwriting 1s and 7s when I was younger, and ended up adapting the cross-through 7s to distinguish it from the 1s. I had the one dolt who would “correct” my handwriting* with big red marks all over the page; apparently originality in choice of letter shape was verboten in his world. I still occasionally get people who are baffled as to why I cross-through the 7 in the first place. I rarely cross-through Zs, but if I’m writing something like an email in my own handwriting, I tend to cross-through 0s to keep them from looking like Os to people.
(*a sample of my handwriting: sorry, it’s a crappy photo and a bad pen.)
In specific cases like this, where Z and 2 might be mistaken for one another, putting a line through the Z definitely makes sense.
But in everyday writing, how common is it to look at someone’s writing and wonder whether it’s a Z or a 2?
I mean, if someone from Manhattan gives me their phone number, i’m pretty sure the area code is 212, not Z1Z, no matter how poor their construction of the figures might be.
And if that person writes a note directing me to a popular tourist attraction, i probably won’t scratch my head wondering where the Bronx 2oo is.
My business is in a rural area. My old address was RD #3 Box 194Z. No matter how we stressed the “Z”, People always wanted it to be a “2”. Thankfully, the 911 system required a change be implemented.
Ditto.