Symbian Signed?

I tried to install new application to my Nokia E71, and found out that it isn't Symbian Signed. I didn't quite get at first what was this "Symbian Signed"...

Now I have a guess what's all about:
Nokia doesn't want that every program what has been written to Symbian get shared. It is wanted to keep some kind of quality in programs, so users can download and test them without fear of them breaking their phones or doing something unwanted.

~ MyLillian