This tradition is still (sort of) in operation here in Austria. "Heuriger" (exclusive in Austria) sell "this year's wine" (where the name comes from). They are not open all year. They are open after the harvest and roughly until the season's wine has been drunk.

Heuriger inform their customers that they have open by sticking wine vine branches over the main entrance door. Once the average public became more literate, the physical branches have been replaced by a sign that reads (in German) "stuck out" (although if you look up the word "ausgesteckt" in a German-English dictionary you'll find the translation "unplugged" LOL), as in the wine vines have been "stuck out" over the main door.

Here is some good info in German:

https://glossar.wein.plus/heuriger

Unfortunately, the English version of the page is really short, but Google translate is your friend.