This one is circulating right now. I found references to it circulating in 2015, 2009, and even as far back as the 60s:
I noticed immediately that this has not been posted by any of my math nerd friends. The second thing I noticed, being someone that’s familiar with medieval manuscripts, is that the “early” versions of these numbers supposedly cited in this “angles” explanation are not early.
So, from my studies of writing, including in how the numbers began to be depicted in Western texts, I knew that this explanation was almost certainly spurious due to the fact that this number set looked more like a modern digital display than anything written with a pen, and depended on that squared-off look (not to mention weird flourishes, such as the foot and cross hatch on the 7 and the extra curl on the nine) to prove its point.
I’ll let the Good Math/Bad Math blog do the honours of debunking this particular Facebook factoid.