Making the assumption you are in the US.You have a copyright to your work the instant it is created. (Unless you have signed it away somehow) Watermarking the image is a way of making it known that you are the creator and copyright holder. It will not prevent unauthorized use by unscroupulous people.To ever claim damages for copyright infringement you should register your images with the Copyright office.
In the United States, the copyright mark on your watermark does have meaning and value: it means you have legal rights to the picture and it prevents others from copying it or using it without your permission. I believe that the watermark isn't even required for you to assert your claim of copyright.
Of course, with digital images, it's very hard to prevent people from copying your stuff, then identifying that someone else is using it and then stop them, and realistically, if you don't want people to steal digital images, you probably ought not to put them online or send them to others. Flickr, Facebook, Instagram and probably others will force people to take down your images if you send Flickr/Facebook/Instagram/others a notice of copyright infrignement with supporting documentation. I have done this several times. The really hard part is finding who is illegally using your images.
You have a copyright to your work the instant it is created. (Unless you have signed it away somehow) Watermarking the image is a way of making it known that you are the creator and copyright holder. It will not prevent unauthorized use by unscroupulous people.
It can be different in each country. In the US, copyright is a legal right that you receive the moment you create your work, regardless of whether or not there is a watermark.
A watermark gives notice of that copyright, but it is not the copyright itself.
A watermark can’t prevent copyright infringement, but it can help deter it. In the US, what helps the most is registering your images with the US Copyright Office because if you take legal action against an infringer, the potential financial settlement for you is much higher if the image is registered.
Because a watermark can only deter (not prevent) infringement, for many photographers a watermark is more valuable for letting people know that they took that photo, so if someone sees your photo on a random website or social media and wants to license your photo, they can see how to contact you to buy a license.
Another way to give notice is to make sure the Copyright field in image metadata has your copyright notice in it. You can enter this for many images at once in the Metadata panel in Adobe Lightroom Classic or Bridge, or for an open image in Photoshop by choosing File > File Info.
Whether you use a watermark, a metadata, or both, they can help you in court because the DMCA law says you might get a higher settlement if someone infringed your copyright when a notice was present.
I am not a lawyer, so if you want more legal details, you should talk to an intellectual property attorney. You can also learn more about copyright for photographers in the US at these two websites: