Is it haram to tie a tiny knot around your finger to remember something constantly so that it becomes habit?

Is it haram to tie a tiny knot around your finger or wear a rubber band around your hand solely for the reason of trying to remember something constantly so that it becomes habit? For example: A man ties a tiny string around his finger to remember him to make dhikr, and after three days, takes it off, for it has become habit. Looking around, I have only found references to indicate that wearing ornaments such as these are normally haram to separate males from females. Would the practice of using an ornament as a memory helper be halal or haram?