Steatoda nobilis and grossa usually (but not always) fall into the category where identification can be made from pattern. Both sexes of S. nobilis usually have a similar abdominal pattern as shown in photographs on this website for the species, with a well-marked example at Steatoda nobilis image, with males usually smaller and adults with the complex palp structure of an adult male. Some Steatoda nobilis females can have hardly any pattern at all, in which case, microscopical examination of the adult is the only way to be sure of identification.
S. grossa males and juveniles have a pattern of white markings similar to those in your photo. Adult females usually have no visible pattern.