Is it possible to trademark a signature?

Register trademark in Vietnam

If you need any evidence to know that this is fact, you can look into the signatures of John Hancock, Taylor swift, John Lennon, Shahrukh Khan or Sachin Tendulkar. These celebrities have gotten their signatures trademarked.

However, as you can guess, most of them are celebrities with the brand being, well, they themselves are a brand. To that end, make sure that whatever you do is a significant brand before opting for this.