A North Korean soldier waves as he stands guard on the river bank of the North Korean town of Sinuiju, opposite side of Dandong, China on Wednesday Feb. 6, 2013. North Korea vowed last month to carry out its third nuclear test but has said nothing about timing. AP Photo/Eugene Hoshiko North Korean soldiers stand guard on the river bank of the North Korean town of Sinuiju, opposite side of Dandong, China on Wednesday Feb. 6, 2013. North Korean children stand on the river bank of the North Korean town of Sinuiju, opposite side of in Dandong, China on Wednesday Feb. 6, 2013. As a result, the building suspense in Seoul has prompted many to look at the dates Pyongyang has chosen for past atomic tests, as well as rocket and missile launches. A North Korean soldier, right, stands with others on the barge on the river bank of the North Korean town of Sinuiju, opposite side of Dandong, China on Wednesday, Feb. 6, 2013. SEOUL, South Korea (AP) - So when will it be? Dates and numbers have great symbolic importance to North Korea's government. So Pyongyang often schedules what Washington calls "provocative acts" around U.S. holidays and important South Korean political events, an effort to send none-too-subtle messages to its main enemies - Washington and Seoul. Pyongyang also uses the tests to give a nationalistic boost to its citizens, often favoring significant milestones of the state, party and ruling Kim family. Here's a look at the "meaningful dates" North Korea has selected for past tests and launches, as well as future key dates on which Pyongyang might choose to stage its third nuclear test: North Korea also conducted missile tests on America's Independence Day in 2006. It launched a long-range rocket just a few months after Obama's first inauguration in 2009. Some speculate that Pyongyang might make good on its atomic threat on the upcoming Feb. 18 federal holiday. That day is Washington's Birthday, also known as Presidents Day. South Korea's foreign minister has also suggested President Barack Obama's State of the Union address on Feb. 12. North Korea also has used inaugurations and elections in archrival South Korea to test its missiles and to launch rockets. Days before that, a North Korean jet also intruded into South Korean airspace over the Yellow Sea, turning back as warplanes in South Korea scrambled. And in 1998, six months after liberal South Korean President Kim Dae-jung took office, North Korea launched what it said was a rocket carrying a satellite. A failed North Korean rocket test last year fell on April 12, days before the April 15 celebration of the centennial of the birth of national founder Kim Il Sung.