Is "The Best Meat Buns" a double entendre in Japanese? Here is a shot from Baby Steps, episode 20 at time mark 16:46:



I think "The Best Meat Buns" is the English translation of the sign Nat-chan is wearing on her back. She is considered one of the prettiest and most popular girls in her high school. She is wearing a maid-cafe outfit for the cultural festival, and her group is selling meat buns. In English the sign is an obvious double entendre. What is the literal translation of the sign? Would Japanese folks see it as a double entendre too?  (Maybe in Japan, "buns" just means buns.)

I think if it is a Japanese double entendre, Nat-chan would be in on the joke. She is not portrayed as just a clueless girl.
You might be overthinking this. 

Remember that this is at a cultural festival. Natsu with the ad on her back, wearing a China dress, is more likely out there to be a poster girl of sorts to advertise her class's themed cafe,inside the building. 

If a double entendre was intended it would make more sense to put the ad on the front versus the back, below the actual goods. Even if this were true, why advertise the class when the advertised product is right there?