This is clipart converted and broken apart that has been released into the public domain because the document says so, and its from NASA, a USA government agency. The publication is called "The Brain in Space:" http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/The.Brain.in.Space.html スペース 科学 脳 58294main_The.Brain.in.Space ページ 98 エスター階段
Sign to mark your stairwell with silhouette of a spiral staircase in art nouveau style, part of a series. 階段 階段の吹き抜け 階段 階段の吹き抜けのドアの記号