South Korea's Dong-a Ilbo newspaper said in a Pyongyang-datelined dispatch that banners boasting about the October 9 test were much in evidence.
"Long live General Kim Jong-Il, a matchless leader building a global nuclear power!" read a huge red banner shown hanging on one building in a front-page picture taken on Friday.
Even a children's nursery displayed a sign reading "Let's take a big leap in building a powerful nation in the spirit of successfully conducting a nuclear test!" it said.
The slogans mostly underline North Korea's "pride as a nuclear power" along with the customary praise for its leader, the newspaper reported.
North Korea confirmed last week it would return to six-nation nuclear disarmament talks after boycotting the negotiations since November 2005.
The decision, only three weeks after the test, was welcomed by negotiating partners the United States, Japan, South Korea, China and Russia.
But there are fears Pyongyang will use its new nuclear status as leverage to seek an easing of US and UN sanctions, while stalling on demands that it verifiably give up its arsenal.
Officials in Seoul, Washington and Tokyo refuse to accept North Korea as a nuclear power.
On Saturday it hit back by declaring that Japan should not attend the talks because it refuses to recognize the North's nuclear-armed status.
Japanese leaders behaved "impudently" by asserting that "Japan cannot accept North Korea's return to the six-party talks as a nuclear-armed state," a foreign ministry spokesman said.
"The Japanese authorities have thus clearly proved themselves that they are political imbeciles incapable of judging the trend of the situation and their deplorable position."
The six-way talks began in 2003. North Korea agreed in September 2005 to scrap its nuclear programs in exchange for energy and other economic benefits and security guarantees.
But it walked out of the forum just two months later in protest at US financial sanctions under which North Korean accounts totaling 24 million dollars were frozen by a Macau bank.