Markers are used in Matplotlib plots to mark the points on a line which refers to a datapoint. All the possible marker styles in Matplotlib are listed here.
However, it is difficult to pick a marker just by looking at its character or its label. I generated the above image as a visual reference to pick markers. It was generated by using this piece of code:
Tried with: Matplotlib 1.3.0 and Ubuntu 12.04 LTS