A favorite activity is to grab pieces of my art and find symbols in them. If symbol seems a rather elevated term, just find marks (which are probably symbols we haven’t figured out the meaning for yet). They can be traced, flipped, enlarged, darkened, put into groups, shrunk.
It doesn’t matter how simple they are ~ as you keep collecting these marks/symbols, you will start recognizing patterns and themes in your work where they emerge again and again. You can create your own catalogue of marks/symbols to grab and use when you have a lonely spot in your work, a spot that is crying out for “something” to fill it. Judicious dabbing with a brush or cloth will blend it in to its surroundings as if it has always been there.
Add these to all your doodles, and you’ll soon have an impressive collection of ready-to-go “digital stamps” to print and use.