timeseries and categorical data

I'd like to chart two time series: closing prices, by day, for a given stock, and a set of buy/sell recommendations for that stock, to see how the stock pickers did

charting the stock closing prices is no problem, but superimposing the buy/sell signals is harder

the way I understand it, the buy/sell signals are a time series of data type categorical. I have encoded them as (1/-1) but they could take any binary form. I'd like to have those signals appear at the correct point on the timeline (x axis) as an up or down arrow, or something like that. how to do this?

thanks