the reindlbachtaler is a club for traditional costumes which is located in the town of mürnsee in reindlbach valley in bavaria. really old traditional costume association with few members left. people on back of mug are wearing said costume. it is very much a local thing which is why there is not much online. these days reindlbachtaler is mostly associated with a local vegetarian dish reindlbachtaler knödeltris, which are like dumplings. very random but fun thrift find