This function is a shortcut which creates a marked point pattern
  from a given point pattern X and a given vector m 
  by attaching the marks in m to the locations of the points
  in X.  If X is already a marked point pattern, then its marks
  are ignored and replaced by the values in m.
  If m is a single value, then all points will be
  given this mark value. Otherwise, m must be a vector
  of length equal to the number of points in X, and
  the point X[i] will receive the mark m[i].
  Use unmark to remove marks.
  Use ppp to create point patterns in more general
  situations.