One source in the country's Yanggang Province who spoke anonymously said the state has banned the movement of people after anti-Kim propaganda leaflets were found, Radio Free Asia reported.
The flyers read, "Let us overthrow Kim Jong Un," the source said.
According to official North Korean records the country's founder Kim Il Sung had said, "Let us overthrow Japan," before leading an anti-Japanese armed struggle in 1937 in the city of Pochonbo, the location where the leaflets were first discovered.
The slogan appeared to be mocking the original motto.
The state has responded by dispatching a team of investigators.
"A rigorous probe is taking place...and in order to track down the suspects handwriting tests are being conducted while people are being interrogated and houses are being searched," the source said.
A second source in North Hamgyong Province told RFA a large marketplace in the city of Chongjin was the site of commotion after graffiti was found on a building wall that read, "Punish Kim Jong Un, the enemy of the people."
"Patrol teams blocked the surrounding roads and banned the movement of people after the graffiti was discovered," the source said.
Concerns about instability appear to have reached North Korea's official media.
Pyongyang's propaganda outlet Uriminzokkiri claimed Wednesday, local time, North Korean defectors were using drones to target statues of Kim Il Sung and Kim Jong Un.
The drones were being dispatched across the China border and attacking statues of the "highest dignity," North Korea stated.
Pyongyang warned, "Those who try to challenge the Sun will never survive," while claiming the defectors were receiving the financial support of President Park Geun-hye, who was recently impeached in South Korea and awaits a final court decision.