Is it possible add signature or water mark on photographs without post-processing? Like add the signature/water mark while capturing the photos. Any settings available?
Yes depending on what camera you have. Did you read the manual?
In a word, no. Cameras don't generally have this feature built in, however there are ways of automating post processing tasks so that watermarks are applied when software downloads the image without the user having to perform any extra steps, it just depends what software you have
Yes. Although, as mentioned most cameras will require some modification.
With a Physical Mask
The low pass filter on the sensor could be augmented to cast a shadow on the sensor. The easiest way I could imagine doing this would be a metal vapor deposition onto the glass followed by a photolithography and etching process to remove the undesired metal. The resulting shadow mask will add a watermark to each image the camera produces.
An additional benefit of this method is that it can also be used on a film camera.