There are some youth football organizations, which require the parents to sign a "Code of Conduct" form.
I believe this is the biggest bunch of BS.
Do you really believe that the parent who acts like a jerk cares about a piece of paper that he/she signed? How are you going to enforce it? What if they refuse to sign it? There is also the legal issue.
There is no legal reason for them to sign anything regarding behavior.
Are you going to sue them if they break a rule? I believe you are looking for trouble if you try this approach.
The majority of parents are well behaved and act like adults, so there is no need for them to sign anything.
This will make good parents become suspicious and possibly take offense as to why you feel they need to sign something.
Then there is the problem parent who you know is going to not sign any forms and if they do, will break all the rules.
You are going to just "fire 'em up" by demanding a signature.
I believe that at your youth football parent meeting set the rules and make sure you follow through if any rules are broke.
It is important you understand the league rules so at the parent meeting you can explain all of your league rules, and any over your own personal rules, to the parents.
Coaching youth football is time consuming enough and the last thing you need is an additional potential problem to be concerned with.