I have been looking the same app on Apple store and I found some interesting app.iwas looking because I want to put the same in my video and timeline too. Some what I have found are: Timestamp It, date stamper, Auto stamper which is cost $9, there is also Photo stamper Pro, Date stamper, Timestamp Camera, Time stamp Photo and Video; this is a good one because you can put a message on it too.
Whatever you want to choose it's up to you which one will work for you.
For Android I have found the Timestamp Camera Basic, APD TimeStamp where you customize the text, and the last one is the Vignette app.
Good luck for creating video stamp,I hope you can find what is best and what works for you among the list I have given. Otherwise you can create a water mark,by creating your one logo with your name in it and use an app to edit and add it tour video or photo like Watermark app.