Yes this is normal, it is just where the belts are joined together. It seems to only be noticeable on large truck tires, though not always. When I used to work at a tire store, there was a customer who wanted all of his tires replaced because of the same "buckle". It took some explaining to say the least.
You are very observant to notice this as you can't be too careful with sidewall bulges because it can indicate a serious defect resulting in a blowout. I think that most tire stores refrain from even patching on the sidewall (though I've heard it can be done safely) and usually recommend a new tire. That is where your tire "certs" (insurance) can be useful.
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