With "Drive on Left" on, I get this.
(http://i.minus.com/iAkU49v2RYGOS.jpg)
The actual sign behaviour is indeed right (trucks were able to move to different cargo bays). I wonder if the choose sign should be placed on the left instead of on the right...
There is an option for left-handed signals, but all the graphics would need re-drawing. That is on the list some day...
(Although, that particular sign looks all right where it is, I think).