The posters, along with black flags, were spotted early Saturday in Balrampur and Baghmundi areas of the district.
Besides calling for observing black day, the Communist Party of India (Maoist) through the posters also demanded removal of West Bengal Chief Minister Mamata Banerjee.
"We have seized the posters and looking into the matter," said a police officer.
Earlier in July, five suspected Maoists were arrested for putting up similar posters.
Similar posters were also recovered on Friday from Kolkata's Maniktala area.