How to delete the duplicate activities created by the signal event trigger.

Hello All,

I have created a business process where I have used a signal event to trigger the process and create an activity based on the filtering conditions. "Product to Qualify" field used in the business process is a comment field which can input any values. The filter conditions that I added in the signal event includes one of the conditions as "Product to Qualify" needs to be filled in.The current process is creating an activity every time the "Product to Qualify"  value is added or modified. I need only one activity to be created anytime this business process runs. 

Attached the business process screenshot for your reference.

How can I achieve this scenario? Is there any field in Activity page which helps to remove the duplicate activities created?

Please suggest me how to implement this above scenario using either business process or client code?

Thanks All,