For OpenStreetMap(OSM) mapping, drawing your memo on paper printed the OSM map is good solution.
You can describe on the paper anything e.g. Line, words, arrow, symbol and illustration.
"OSM sketch" realize such paper mapping on smartphone.
You can draw on OSM map anything you want to memo anywhere, anytime without printing beforehand.
Operation is easy and optimized for small screen.
Multi touch operation ,scroll and zoom, can be executed also during "drawing mode" so you can pull new canvas out quickly.
To display current location and zoom in/out map support your mapping and these function are difficult for paper.
The drawn line exchange into GPX file and upload to your OSM account page.
You can open the GPX file by PC OSM editor(iD, Potlatch2 and JOSM) and edit OSM data based on your lines when you return your home.