If you want to make other people unable to see what you have liked, you should choose that option in your privacy settings: choose an option “me” in "Who Can See the Videos I've Liked". But we don’t recommend you doing that if you want to promote your content: when people can see the number of thumbs-up each video has they will more likely want to check out the rest of your content. The numbers are extra important when it comes to promotion and nobody can deny that.