signachore
What scratchin' out yer John Hancock often becomes once you get significant Arthur Itis.
If scribblin' on da dotted line is a real signachore, there are at least two fairly-easy options: either obtaining a rubber stamp with your "self-scrawl" imprinted on it (to prevent fraud, this potentially-super-valuable device should be kept under lock and key except when you're actually using it, of course; it may also require a co-signing witness for da stamped name to be legally binding/acceptable), or have a more-able-bodied fellow human grasp your hand to guide it through the writing process (this again necessitates da assistance of another, but if your muscles/joints are truly so weak/stiff/painful dat you can't even occasionally jot down a few words without great difficulty, then you might wanna have a full-time caregiver at your side, anyway, to help you perform ordinary day-to-day tasks more safely/easily).