\picsquare is a simple macro that gives a little square dot with its
center as the reference point. The size of the square is dependent on the
currently effective \thinlines, \thicklines or
\linethickness... declaration. Most of the commands described earlier
that plot little dots, use this macro3. It has been provided
primarily to be used in conjunction with \putfile command described
below.
Only \picsquare has been made accessible to the user.