Hi! If you are using an Android phone then I would suggest you an app named "Video Stamper: Add Logo, Timestamp & Text on Video".
The application will allow you to add your name to the Gallery videos. You can also add Logo to the video by Watermark Logo option. The app also provides Date and TimeStamp, and GPS Stamp.
So, from this app, you can add Signature to the videos.
Hope, this works out!