Hi there,
If I'm not mistaken, this tag [SECURED] is applied through the form properties where you apply a password for the PDF.
In LiveCycle Designer, go to the following:
File > Form Properties > PDF Security and then if a password is set for the form, you can modify the Changes Allowed option to any applicable.
I am not aware of any other way to have that [SECURED] tag.
I hope this will help you.