Jodekager means "Jewish cookie" and is a well known Danish biscuit, especially (ironically) around Christmas.
"Bagt i gasovn" means "baked in gas ovens."
The reaction has been that perhaps the sign was in bad taste but many liked it (and favorited it on Twitter and "Liked" it on Facebook.) Others thought it might be Photoshopped, which is certainly possible. I couldn't find an original image with camera information.
Even if the sign itself is fake, the reaction is troubling, to say the least.
See "Never to Wait" blog.
(h/t Israel Muse)
UPDATE: Commenter Akusia reminds me of this story from 2005:
A group of Danish Muslims refuse to eat traditional “Jewish” cookies because they feel offended by the name.It all equals out. Jews are offended by gratuitous Holocaust jokes, and Muslims are offended by - Jews.
UPDATE 2: Follow-up at Never to Wait:
Since I wrote the original post, denfri.dk reported that this picture originates from a Dagli’Brugsen in Thorsager, Denmark. Dagli’Brugsen is a the Danish equivalent of a Sainsbury’s Local, and the sign was reportedly put up by a young employee as a joke. As there is only one picture circulating the web, I’m assuming that this sign was taken down immediately, if it ever actually existed in the first place. For this reason, I have not denounced SuperBrugsen in any way.
Martin, a representative from SuperBrugsen, posted the following on their official Facebook page:
We are currently investigating the case, but for now it looks like a tasteless joke. The picture has nothing to do with SuperBrugsen. We would see it as entirely unacceptable for a sign like that to be used in one of our stores.