Hi michaelo,
doodle 
= an aimless drawing;
scribbling or form of sketching performed unconsciously or
semi-consciously, when otherwise engaged or simply bored,
such as while listening to someone on the telephone or during
a lecture.
to
doodle = make a doodle; draw aimlessly
scribble 
= careless hurried writing; meaningless marks and lines poor handwriting;
an aimless drawing
to
scribble = to write hurriedly without heed to legibility or style;
to cover with scribble, doodle, or meaningless marks and lines
scrawl 
= Irregular, often illegible handwriting.
something, such as a note, written hastily or illegibly.
to
scrawl to write hastily or illegibly;
to write in a sprawling, irregular manner.
Regards.
V.