Not that I know of. Look at the TOS and rules. I don't think you do though.

no you dont have to. i just signed up and i have a sig. some forums however restrict members from having signatures until certain post count or reputation level is reached but if there is such restrictions, the signature would be disabled by admin by default. if it is available and showing, it is my understanding that you can use them

As long as your going to contribute go for it. As above I joined yesterday and Have one.

No you don't. Go to this URL to edit your sig.

http://www.warriorforum.com/profile....=editsignature

Might be a good idea to read the rules on signatures before you do that. To find that link, click on the User CP link in the upper right above the threads. Click on Edit Signature and enter the sig you want in the dialog box.

Don't forget the rules, like no affiliate links, and I think you are limited to five lines, but I am not an authority on that rule, so best to check them for yourself.

Definitely not necessary. However, be sure to read the rules and guidelines about what exactly you can link to.