I would have to assume that the project team people would only see a
printed copy of the form. Otherwise, the name would show up in the
formula bar and this effort would be for naught.
If they will see only printed forms, then what you probably need is a
font that shows asterisks or some such for every character entered.
That is, an 'a' would look just like a 'z' which would look like any
other letter. I'm not sure where you can find such a font, but I
imagine there must be a free one out there somewhere. Just make sure
it's on every PC that would print one of your forms.
An alternative would be to Conditional Format both the the font color
and the cell itself as gray if the cell is not empty. This tells you
there is something entered in the cell, but only someone who is looking
at the form in Excel can select the cell to see who actually "signed"
it. There is also an advantage in that one can't tell from the
printout how many characters is in the signature as there is only a
gray cell and not characters that someone can count.