How to add Icon in pdf for show validity of a digital signature in C# using Itextsharp

I have signed a pdf document with use of itextsharp.

I want to add Icon for Signature validity. how can i add icon like as in attached image.

When certificate is unknown origin then display want to display "?" and validity known then want to show "✔" is it possible to add this in pdf files.

is there any PDF Viewer functionality for displaying icon for validity of a signature.