Could you produce a picture of this sign? And I do know the code and have posted it for you before. Here it is again, please notice the term no casual jeans. That would infer that non casual jeans(whatever that is) are allowed.
"Recommended on board clothing is resort or country club casual. For evening dining, elegant casual resort wear is suggested. We request that casual jeans, shorts, t-shirts, baseball caps, sandals, or tennis shoes not be worn in the restaurants after 6 PM. Baseball caps may be worn in the Terrace Café after 6 PM. "
For additional dress code guidelines refer to the onboard Currents.
In full disclosure I do not wear any jeans to the GDR or Specialty restaurants, but I've seen many people over the years wear nice jeans in Oceania's restaurant that look much better than other people's K Mart duds that are completely within the guidelines.