The joke is a play on words.  Typically on products or decorative pieces there may be written on the item where it was produced, for example it might say 'made in Japan'.  The woman wearing the kimono in the picture may have been a maid, or a house keeper or house cleaner, living in Japan.
One item contributed was a picture of a pretty , kimono - clad girl ; it bore the inscription : ' ' Maid in Japan ' ' .