What "script" are you using for doing txt2img? The watermark function is automatically called when you use the CLI in two places, https://github.com/CompVis/stable-diffusion/blob/69ae4b35e0a... and https://github.com/CompVis/stable-diffusion/blob/69ae4b35e0a...
Trivial to remove, I give you that. But AFAIK, the original repository + most forks put the watermark automatically unless you've removed it on your own.