It’s easy to tell when a plumber or an electrician is hard at work. They’ve got parts and equipment all around them, they’re doing things to other things with tools and things, and you can tell when they’ve finished because there’s a working thing where there wasn’t one before.
It’s still fairly easy to tell when a teacher or a scholar or an accountant is hard at work. They’ve got piles of books and papers, or they’ve got lots of computer files, and they’re writing on them or typing in them or reading them, and you can tell that they’re finished because when they’re done, they stop.
Writers, though . . . writers may have piles of paper and lots of computer files and lots of books scattered all around, but at any given moment they may be staring out into space, or playing Solitaire on their computer, or putting together the world’s longest paper-clip chain, and maybe they’re just goofing off, but on the other hand maybe they’re off somewhere inside their own heads working out the final twists on the plot, or trying to come up with the perfect opening sentence.
And there’s no way to tell from the outside which is which.
It’s a wonder our friends and family and household pets put up with us sometimes, it really is.
Dr. Doyle's Blog 
I once read an article that advised writers to have a special writing hat/coat/gloves/other that they put on each time they were writing so that it was clear when they were working even if they looked as if they were not doing anything important.
The downside of course is that it risks becoming something the writer thinks they need to work. like a favourite pen.