I hate rattling on the door of an occupied toilet, especially if the poor person inside says Won’t be long. I also hate when someone else does it to me. You are meant to be able to tell from the button under the handle which indicates red if locked. It is at the wrong angle for me to see it, especially if I am hauling a drip stand with me.
So my semi solution is I have my personal engaged sign which I carry round with me.