... or at least a certificate of authenticity, that was made by UN. However, without a good picture of the movement, I fear it is difficult to say anything about it. Generally, UN was famous for its complicated watches and chonometers. This watch does not fall in any of these categories, so it is presumably not something I would expect to purchase a house from its sales result (well, a tree-house maybe ...). However, if the movement is really well finished and rare, this might be different.
Best regards, and thanks for showing the watch!
Marcus