For Americans:
http://www.mental-health-today.com/gender/work.htm (http://www.mental-health-today.com/gender/work.htm)
she mentions simply circulating a memo to all fellow workers that the person will be transitioning on a certain date. this is almost the same as putting note on notice board that I did.
advantange of being open about it is that no-one can complain they don't know they have to use the new gender and name.
A notice was posted in our lunchroom, while I was on vacation. Upon my return I was full time and the store employees were informed.