Sort of makes you wonder if the physical act of writing it, like with a pen, mattered. The hand moving to draw that same symbol every time could have locked it into your muscle memory in a way typing wouldn't. The body holds onto stuff the brain tries to shake loose.
Read about a study on this exact thing. It said writing by hand makes your brain work harder to form the shapes, so you remember better. @reed.nora's point about muscle memory fits that perfectly.