|I read this tip in an issue of Vogue Magazine many years ago and wanted to share my slightly-modified-with-the-times version on PR.
If you're like me, you can never remember what size or type of needle is in your machine(s). And forget trying to read the size off the needle end with a strong magnifier--even if you succeed this far, it won't tell you if its a ball-point/stretch, universal, or sharp/microtex point. (I think the color of the needle end may be helpful, if you could remember what color means what.)
I started sticking post-it flags (mine are from Office Depot and are 1" by 3") to my sewing machines and serger in the vicinity over the needle and out of the way of any buttons and displays. The flag states the needle size and type of needle point. If I'm using a titanium needle, I write this too, since I store these separately from my other needles.
If I'm halfway through one project and I start working on another using another needle size, I remove both the needle and flag and secure them in a project bag with the rest of the project till I'm ready to work with that project again.
Now, I always know what my needle size and type is. The post-it flags are easy to stick and remove several times and they don't leave a residue on my machine.