Ah yes, I probably get at least one customer a week with the same question. The technical term for this is called undulation. We keep a poster in our waiting area, showing this condition, to help explain it to people. I always recommend that if you can't tell if it is an indention or a bulge, to feel with your hand on the backside of the tire. Undulation will be present on both sidewalls of the tire in the same place. As Bfezel posted previously, undulation is purely cosmetic, and will not hurt the performance of the tire at all.
A tire with broke cord (bulge) will just be on one sidewall, where the cord is broke.
Some tires will have several undulation places on them. I have seen 4-5 on many tires.
Here is a pdf file from the Rubber Manufacturers Association about undulation.
https://www.rma.org/getfile.cfm?ID=376&type=publication