As far as I can remember I've never run into a signed open source project. If I needed it signed for some reason, I signed it myself. I can't really see an advantage to signing an assembly as such. If you're worried about the pre-compiled binary version being signed, then I would say just project management should have that key. A person creating a signed project though should be fully capable of adding the source code to their project, or creating the project's necessary signing and compiling it for themselves.
