Watermarks are only an issue in-as-much as it is used to trace down which copy was leaked.
With modern digital projection systems; you don’t get a reel of film; you get a briefcase of [SS/HD]Ds containing the raw, encrypted, footage. The digital projection system will decrypt using provided keys. There’s no output except the standard ones for the theatre projectors and sound systems…so capturing the output is difficult.
If you do intercept the signal; the projection system might detect it; and refuse playback or wipe the decryption keys. Watermarking is also a danger; since your theater can get identified as the leak source and sued.
It occurs to me that adding a visual watermark might actually serve to obscure a visual watermarking scheme that is otherwise invisible by providing data that scrambles or breaks the watermark decoder itself.
Audio watermarks can be distorted in any number of ways; and it could be that some of the wildly poor audio quality in most cam-rips is probably the only way you can defeat the watermark; by using a LQ microphone and encoding the audio to a very limited bitrate and then re-upsampling; to defeat any subtle alterations a digital watermark might make to the audio waveform.