1.7 What needs to be shown for the complainant to successfully assert common law or unregistered trademark rights?
WIPO Overview of WIPO Panel Views on Selected UDRP Questions, Second Edition ("WIPO Overview 2.0")
Not a legal opinion or advice. I was just curious as to the WIPO UDRP precedent. You can sue anyone you want in civil court -- costs $100 in filing fees (about).