Cidu Bill on Aug 27th 2008
That’s a mezuzah, which Jewish families place next to their doorways (sometimes next to the doorways of each room inside the house or apartment, as well). There’s a scroll inside the mezuzah, on which is written the Shema, an important Jewish prayer.
The comic is portraying it very accurately, right down to the angle at which the mezuzah is supposed to be positioned.
Knowing all this, however, doesn’t explain the actual joke (though the concept itself is pretty funny, if a bit obscure to many of the non-Chosen).