btw i have found the way of having two container fields one on top of the other and one selectable and one not.
don't know if anyone knows a better solution
There are likely many ways to approach this one. Here's a potential solution: have the container fields in their own table, with a one to one relationship to allow someone to add a new record/signature.
You can configure security such that you can create but not edit records in that table. Now when someone adds their signature, it creates its own record and is subject to the security policy associated with it.
You may also want to put some UI in place to safeguard against users that are in with full access privileges if you need it.
Again, just one approach.
beautiful suggestion mate, thanks so much