点の形 (shape) を変える

ggplot(dat, aes(x=xvar, y=yvar, shape=cond)) + geom_point() +
    scale_shape_manual(values=c(1,2))

Scatterplots (ggplot2)) http://www.cookbook-r.com/Graphs/Scatterplots_(ggplot2)/#set-colorshape-by-another-variable