title: how to plot arbitrary markers on a pandas data series?
body: <p>I'm trying to place marks along a pandas data series (to show buy/sell events on a stock market graph)</p>
  
  <p>I'm able to do this on a simple array that I create using pyplot, however I can't find reference as to how to indicate arbitrary events in a pandas time series.</p>
  
  <p>Perhaps pandas doesn't have this functionality built in.  Could someone provide help in the way one would take this series and add some arbitrary marks along the curve...</p>
  
  <pre><code>import datetime
  import matplotlib.pyplot as plt
  import pandas
  from pandas import Series, date_range
  import numpy as np
  import random
  
  
  
  ts = Series(randn(1000), index=date_range('1/1/2000', periods=1000))
  ts = ts.cumsum()
  
  #--  the markers should be another pandas time series with true/false values
  #--    We only want to show a mark where the value is True
  tfValues = np.random.randint(2, size=len(ts)).astype('bool')
  markers = Series(tfValues, index=date_range('1/1/2000', periods=1000))
  
  fig, ax1 = plt.subplots()
  ts.plot(ax=ax1)
  
  ax1.plot(markers,'g^')   # This is where I get held up.
  plt.show()
  </code></pre>