Written in black ink, the poster was pasted on the boundary walls of the playground of a high school at Bishnupur under Rajarhat Police Station in North 24-Parganas district.
The poster said the outfit would use an 18-year-old girl as human bomb at the crowded Sealdah station.
However, there was no mention of any time of the blast, district police sources said adding the matter was being investigated to see if it had any link with the Burdwan blast case.