We all learn pretty quickly that there's a difference between a left pedal and a right pedal. What we don't learn so quickly is how to tell them apart. On nearly every pedal, there's either a small "R" or "L" somewhere.  Key words being "small" and "somewhere."  But there's a way to tell them apart without your reading glasses. Except for Shimano's offerings, nearly every left pedal on Earth has a mark on its spindle to tell you that it's not in the right. Most have a single indented line surrounding the the spindle, right at the base where it flairs out to sit against the crank. Others have parallel knurling lines that flank the wrench flats. But both are easy to see with a quick glance. Just make sure they thread in straight.