Details: This poster says "That's what she said" in white lettering against a blue background.
That's what she said is a phrase used in response to an accidental double entendre, especially one that is sexual in nature. A double entendre or adianoeta is a figure of speech in which a spoken phrase is devised to be understood in either of two ways. Often the first meaning is straightforward, while the second meaning is less so, often risqué, inappropriate, or ironic.
This poster is usually printed with a thin white edge border.