You may (a better word would be 'should', but read on) need the signature of the course coordinator to drop the course. With the course withdrawal form I did at UNSW, it stated that I had to fetch the signature of the coordinator of the course I was dropping, but I visited my home faculty first to get their signature, and the faculty bloke told me not to worry about it and dropped the subject for me on the spot. So, in theory, yes, you need the signature and the course coordinator of the course you're dropping will know, but maybe in practice you don't her/his signature.