Your lane position should clarify your intention. Normally, you should be in the left lane (if there are more than one), and at the left side of the lane to make the left turn. You may have to merge early to get to this position. In this case, motorists will understand your intention. (They may not respect it, but that's another issue. I had one motorist pass me on the left at twice the speed limit - I don't think he cared about hand signals or traffic lights.)

If you are in a bike lane at the right side of the road, I suggest you leave the bike lane before your turn. (I wish this were hypothetical - a number of traffic planners here tell me I should always use the bike lane, and have to turn left from the right side of the road if a bike lane is present. I am not a fan of the facilities they install.)