OK time for a confession.
I have trouble indicating left.
Yes, after years of cycling I still feel a little unsteady not holding the handlebars with my left hand, so I either (a) don’t indicate at all and hope my left lean and slow-down gives the appropriate signal; or (b) I jerkily lift my arm for about 2 seconds before I turn.
Perhaps the Seil bag by Lee Myung Su design lab is the answer. The backpack is designed to show left and right turn signal of a bicycle rider by controlling the detachable wireless controller. The lights might be a bit distracting for drivers not used to seeing the pretty patterns, but it’s a nice idea!