> head(mktdata)
           SPY.Open SPY.High SPY.Low SPY.Close SPY.Volume SPY.Adjusted sma
2000-01-03   148.25   148.25  143.88    145.44    8164300       117.72  NA
2000-01-04   143.53   144.06  139.64    139.75    8089800       113.11  NA
2000-01-05   139.94   141.53  137.25    140.00   12177900       113.32  NA
2000-01-06   139.63   141.50  137.75    137.75    6227200       111.49  NA
2000-01-07   140.31   145.75  140.06    145.75    8066500       117.97  NA
2000-01-10   146.25   146.91  145.03    146.25    5741700       118.37  NA
           sigCrossover.sig sigCrossover.sig.1
2000-01-03               NA                 NA
2000-01-04               NA                 NA
2000-01-05               NA                 NA
2000-01-06               NA                 NA
2000-01-07               NA                 NA
2000-01-10               NA                 NA