We do not place any watermarks on any finished render.
We suspect the media player you are using is displaying the filename. Check the properties/preferences of your media player to see if you can change a setting.
For example, VLC will display the filename and you can go to >> Tools / Preferences / All / Video > Scroll down to and uncheck: 'Show Media Title On Video' > Save.
The next time VLC is launched the video title should not be displayed.
You can also "rename" the file name yourself completely by "right clicking" on the file once you have downloaded it to your computer.