It is easy to do this for a particular cell by using the isnumber or isblank formula. I don't know how to do this for a range or group of cells. It isn't as easy as it would seem.
An option would be to use conditional formating (in the formatmenu) to show a red pattern on cells that contain a particular value that you could set as the default. You could pick a number that would be unlikely to be used and then copy that format to all the cells that need data input into them. The boxes will stay red until data is entered.
Another way to make sure data gets entered into every cell is to create a data entry Worksheet, in this case one for each member or the dept. This way you can simply scan the data entry sheet and quickly see if there are any blanks. It is easy to then create a formula in the destination cell that enters whatever is on the data entry page.
You may already know all of this but if not hope it helps!