I'm guessing this is part of a sentence, rather than a signature space at the bottom of a document, because you've put "rechtsverbindlicheN". Could we have the context, please?
"Authorised signature" is the more usual term if this is an individual signing on behalf of a corporation. And if you do use "legally binding", it has no hyphen because "legally" is an adverb.
We've actually had this before, but I suppose the context could be different:
http://www.proz.com/kudoz/german_to_english/law_contracts/74...