I rephrase the question to make it more precise:
If I want to use the Lock dictionary of a signature field the following things need to be done:
1. Insert a 'signature field lock dictionary' as an indirect reference
2. All fields which should be locked are put into the 'Fields' attribute (Action=Include)
3. Now (and that is the question) do I need to set the annotation flag (F) at bit position 8=Locked for each field listed in the 'Fields' attribute, too?
4. Does it furthermore include to set the LockedContents (for each field), too?
Or are both flags totally unrelated to the 'Lock' dictionary functionality?