How to disable the Statement link icon (square with a cross in it, the X on the process activity, Blank statement links) which is appearing on all the activities in Tibco Nimbus?

Disable/Enable Statement link icon from User Group Properties in Tibco Nimbus.

Production and Test

You are able to see this Statement link icon (square with a cross in it) on each activity because in one of the specified group  "Statement Link Indicators (Author)" options enabled so all activities will show this.

To disable this option please follow the below steps
--> go to Tools>> User Accounts >> Right click on Group  >> Properties >> Permission >>
--> Under the permissions tab, Unchecked  "Statement Link Indicators (Author)" option.
--> Re-login to Tibco Nimbus Author Client to check if the Statement link symbols are disappeared from all the activities.

Please note that this is the Tibco Nimbus feature where you can enable blank statement links for all the activities in the Tibco Nimbus.
You can refer to the "Group Permissions" topic in the Tibco Nimbus User guide for more details.