How can I tell if a steel rod is for sharpening or honing?
If it's a rod, it's for honing, not sharpening.  As stated in this article from Serious Eats:


  One of the biggest misconceptions about the particular type of kitchen tool you see above is the belief that it's a knife sharpener. It doesn't help that many manufacturers sell their honing steels as such. But a honing steel is not a sharpener. Ridged, rod-like honing steels, or "stropping irons," as they're sometimes called, do not sharpen blades; they realign them.