It just means you've done something right on that webpage which enable you to secure that position, nothing more nothing less.
And you could be anybody; even some 15 years old can achieve top rankings.
A sign-in seal is a personalized image or a message that will only appear on genuine Yahoo pages.
That shouldn't be their main selling point and they should've known better.
Unless they are trying to impress all those people who don't know any better.
I came across several posts in Google Groups at decided to do some digging about this company.
I am not here to pass judgment, nor do I want to argue about any particular point of view.
Plus, the free Yahoo Sign-In Seal will help protect you from password theft, also known as phishing.