My father died in November and as Jews, we wear a crea, a black ribbon that has been ripped, for a period of 30 days. Orthodox Jews may wear it for up to a year, It does not have to be visible to the outside world, that is a matter of preference. It has its roots in the biblical instruction to “rend your garments as a sign of mourning”, I am not sure of the citation.
The workplace is a different situation. I understand the symbolism of mounting the white ribbon in honor of the deceased and as a sign of support for your co-worker. My only comment would be that some people carry their visible grief longer than others. An employee who has lost a loved one might take great comfort in seeing that ribbon every day, but for other employees that ribbon might remind them of their own issues and that might be counterproductive.
I guess what I am saying is that you have a nice gesture there, something I have never experienced in my 35 years in the workplace, but you should put a finite limit on how long the ribbon stays on the door. For matters of public mourning, we may fly the US flag at half-staff for thirty days and that length of time seems about right for the ribbon on the door.
SRM