When I first started in photography all my shots had a watermark on them. It didn't cover a large portion of the photo and was slightly faded as to not distract from the content.
Recently there have been a couple of occasions where I have found my photos on social media sites and normal websites without the requested credit links or even just my name.
I do ask everyone who uses my shots that they have a credit attached to the content, whether its a post on Facebook or part of a performers portfolio. a working, click-able hyper link back to my web page is sufficient.
Those whom I have contacted have corrected the oversight when requested but it is not something I should be asking. From now on I have decided to reinstate by watermark on all my photos.
It is small and unobtrusive so wont get in way of the content. There are other ways to protect my copyright, I have the original files with date stamps and metadata plus I can always embed more information with a stenography program. I will try that and blog about it.
Below is a picture I took at Madam Jo Jo's recently. You can see the watermark at the bottom right hand corner.