What to make of electrical rating etched into circuit breaker?
I have a variety of old and new Square D breakers in my panel. It seems that the older ones have this type of rating on the handle, while it is printed on the newer ones. I'm not sure what the cut-off would be in terms of age / production year, but it's not important.
It looks to me like that breaker is rated at 15A, and the etching is factory-applied, not done by someone after the fact as you suspect. You could check the side of the breaker if you can turn the power off and remove it to be sure the ratings there match the handle rating. I just checked a spare breaker and there is no other place the amperage rating is expressed anywhere on it. The only place I could find is the handle.
Here is a picture of my panel showing the variety of ways the rating is printed on the handles:

Upon reading harper's comment, I checked a spare 30 amp breaker I have to see what the other info on it reveals in more details. Stuff stamped on the side is all related to terminal ratings. There are also a couple of stickers, but those do not reveal the trip rating either. The part number is very well hidden, on the bottom of the breaker, in a slot between the line terminals. In my case, it says 235-07. Square D lists this breaker as part number QO235. The product page lists all the details you need, and is easy to find with an internet search for the number and brand of the breaker.