Schlemmerwoche: Participating Winery
This is one of the wineries participating in the "Schlemmerwoche" ("week of feasting"). As a sign (so that people know) they have this wreath hanging outside with the wine bottle (the "Rheingauer Flöte") together with a glass.
You might actually see this throughout the whole year, not only during the "Schlemmerwoche". It's quite common that wineries open their wine cellars, but they usually don't have that many extra special events like they have during this week.