How can I stop TinyMCE from converting my HTML entities to characters?

Here’s the problem: I paste the HTML entity code for, let’s say, a service mark () into the HTML view of the editor. As soon as I switch to the “visual” tab, my entity code is turned into an actual service mark character (I guess the corresponding UTF-8 character or something? I don’t know from character encodings…). I don’t want this–I want it to stay as the entity reference.