I saw these yellow signs this morning on all the shops on my street that are still open – the pharmacy, the drugstore, the supermarket. It is a thank you to the people keeping the shops going and calls them true heroes. Yes, the commitment, often the humor, and the sheer hard work they have been putting in for the last five days or so are indeed heroic.
ecbinvienna 
Thanks so much for the update. I will share this with my Viennese friends!