A "handwritten sign" is a sign that is made by writing on paper or other surfaces using a pen or pencil, rather than being printed or created on a computer. Full definition
Simply head to the north east of the island on scooter and you'll find a small handwritten sign on a plank of wood, directing you into the jungle. (tripsavvy.com)
They showed up with handwritten signs denouncing Jews as Satan's children, promoting Nazi propaganda and they stood together in Nazi salute chanting, «Blood and soil!» (relevantmagazine.com)
As one supporter's handwritten sign read, it's a TSONGA TSUNAMI! (si.com)