I don’t really agree with this. If you know you have a tendency for flashes of inspiration, what you need is a way of recording those flashes of inspiration on something portable that you can take home with you and continue working on later. A (paper)notebook, serviette, cigarette packet or an envelope, used in conjunction with a pen or pencil is far more practical than a dry erase marker used in conjunction with a table in a cafe or the window of a train.
Carrying a dry erase marker around, to me, indicates one flash of inspiration too few.
Yeah, you need a dry erase marker and a glass cutter.
I prefer a glass etching pen. Dry erase marker tends to smear when I’m cutting out the glass.
I’m mathtarded and bought one especially for doing math. There is something about changing the perspective that makes me less liable to make careless mistakes (most often, performing the wrong operation in a complex problem). I also used it for particularly difficult Latin translations for the same reason.
Well, in John Nash’s case, that much IS true. 
Fair enough. The one that annoyed me in particular was an episode of House where they used a glass “white board” to record symptoms, and as they were trying to correctly diagnose the disease they kept coming back to the damn glass white board and ponder the symptoms which were written in relatively every day type language.
So, mathematicians shouldn’t use blackboards? or whiteboards? It’s not just about documenting the flashes but working through them.
And I’m just relaying what my friend actually does, not what he should do. The OP wanted to know if anyone did X, and I gave an example of someone who does, indeed, do X.
I was lucky enough to attend a Scottish secondary school with a rather good maths department. There was thus the year - twenty odd ago - where I placed very highly in a national maths competition and two other pupils did reasonably well in a less competitive one (which I should say I hadn’t bothered to enter). The town’s local newspaper thus duly ran a story about our collective success. Which involved dispatching their photographer along to take a picture of the three of us and his brilliant “artistic” idea was to have us standing behind a window with me writing an equation in reverse on the glass.
Hardly an example of mathematicians actually writing on windows, but evidence that some people have long thought that that’s the sort of thing they do.
Come to think of it, I’m not sure that I’ve ever seen a mathematician or a physicist actually ever scribble equations on the proverbial napkin while we’ve been arguing in a restaurant or bar.
Of course they should - if they want to. My point is that carrying a dry marker around - specifically as a precaution for recording flashes of inspiration - is probably less useful than carrying a pen or pencil.
loosely-related aside:
At the Salk Institute, architect Louis Kahn put blackboards in the outdoor stairwells, so that the scientists would be encouraged to share ideas with each other spontaneously.
I’m not a mathematician, but while in the shower at the past place I lived, I often worked equations on the fogged up shower door when I had something on my mind. Now I have a shower curtain, but still do math on the inside of the shower wall at times. It’s often not visible, but I can remember the numbers better than if I try to do it in my head.
The only time I’ve seen this was in the study rooms at the library, and that’s because they didn’t have a whiteboard.
??Mathematicians presented their peons to each other?
It was the letter ‘i’.
The breeze, it follows wherever I go.
Mathematicians presented their pines to each other?
If the pines were woody.
We write on the office windows sometimes, since there’s alot of windows and the white board gets filled.
I found out the other day though, that if you write something up there for future reference, you better use it before the sun goes down, as its hard as hell to read when its dark outside.
This I see at least every couple of weeks, and it’s occasionally even me doing it.
And I’ve also seen folks writing on windows, too. In one case, it was because the fellow in question didn’t have a whiteboard near his desk, but did have a window. In the other, there is a whiteboard present (in a communal area), but a lot of people use it and it’s often full, and there’s a huge expanse of windows next to it.
And carrying around dry-erase markers is good for more than just the occasional flash of inspiration, too: Many academics often find themselves in a situation where they’re expected to write on a whiteboard (lecturing to a class, for instance), but you can never count on the markers present in any given room to work. So you bring your own markers to class, and if you then happen upon an appropriate surface on your way to or from class, you can take advantage of it.