Thanks for taking interest in GroupDocs APIs and posting your concerns.
Please note that both (GroupDocs.Annotation and GroupDocs.Signature) APIs are UI-Independent.
GroupDocs.Signature for Java allows you to significantly sign electronic documents. You can add various kind of signatures in a document such as text, image or digital. See details here. API doesn’t provide any such feature to display list of applied signatures in a document. However, you can achieve this at your code level. Whenever user signs a document, save that information (username, document name, signature type etc) at your end and next time when same document is being opened in the application, signature details/list could be retrieved from data source against specified or opened document. There could be any other business logic in order to achieve this scenario.
In GroupDocs.Annotation for Java when a user add some (text, image etc) annotation, he/she can set creator name in the code and that will appear with the annotation. However, in GroupDocs.Signature for Java you cannot set name and date as a default setter property of the API. There are no such properties.
Using GroupDocs.Annotation API you can just annotate documents. Please see feature details here.
For further inquiries regarding GroupDocs.Signature, we’d encourage you to post here.