You can use websites like DomainTools to look-up up information about your domain. Information like the Registrar and Name Server can be indicators of your domain’s provider.
More technologically savvy users can use their computer's Terminal program to look up the domain’s name server by typing in dig -t NS [your domain]. For example, ‘dig -t NS bitly.is’. A domain’s name server can be a good indicator of the domain provider but is depended on the provider’s naming methods.