hei'ya Nicholas, welcome to the forum,
personaly I haven't done a lot of wood modeling,
but maybe a drawn "block" for the representations,
and placing that in the direction, as an indicator
I guess you would use different block styles for different woods,
or cuts- rotary, planed or quartered etc.
hope this helps- have a good'n kelef
edit: I am guessing that you don't want to use the
wood appearance? and then display shaded in
the drawing- you could edit this to do the grain
I drew a block showing direction for graining in metalwork. It's easy to resize for scale as well as rotate. Inserts in a second too.