Activity Diagram:To show the acknowlegment which notation is used

UML
#1

Hi

I am working on activity diagram for my project. I am little bit confusing that to show acknowlegment Signal notation is used or Action notation.

#2

Thanks for your message. I’m sorry that I don’t quite get your message. Do you mean you don’t know when to use Signal, when to use Action?

Best regards,
Rain