Beware of Your Mark
Markers can contain harsh chemicals (evinced by their strong smell). Because toxic chemicals can leak into the groundwater from the landfills at which they're disposed, it's better to use markers that are water-based and have nontoxic ink with refillable heads.
Additional Information:
Did you know that SAC/the Workspace in the Memorial Union has Texas Markers available for use (which are refillable capillary pens)? These are great for making banners or other large print signs.