The sign "dekoriert" in Germany and also in Switzerland means that there will be Fasnacht/Fasching/Karneval decoration in the venue, mostly in Restaurants and Bars. Only decoration - nothing else implied. You will find those signs on the most boring and conservative countryside family restaurants just as well as downtown bars that open at 23:00 and close at 4:00.
These signs do not indicate any price changes or any kind of events happening in the bar. Unless there are city-wide carnival activities on special days of the year, you should expect there to be additional information when there is a special (public) event related to carnival. This can include live music or shows. Some parts of these shows might look to some like "naked girls", but they are more clothed than the actually topless or even completely naked girls in some Brazilian carnival parades.
What to expect inside a bar during carnival goes pretty much under the same principles as outside of carnival: If there is a special event, they might charge extra. If they do not show fully naked or topless girls normally, the chances are very slim they would do so during carnival either.