In what way is Amazon's DRM "broken". It works fine on all 3 of my Kindles. Or, do you mean that is is possible to remove the DRM? All DRM is removable, as far as I know, if you know what you are doing.
I suppose by watermark, you mean embedding some text in the book saying who the owner is. Yes, you can do that, but you have to recreate the book every time in order to add the text.