They're service stars. I don't know about the other branches, but in the army they basically note how many times an award was received.
An anecdote from online that describes the difference between a bronze star and bronze/silver service stars for those who may not know.
"A Bronze Service Star it is an attachment worn in conjunction with another medal. The Bronze Service Star is worn on the campaign ribbon, such as the Asiatic-Pacific Campaign Medal and denotes the person’s participation in a specific battle, engagement or offensive.
I looked at my father’s Asiatic-Pacific Campaign Medal and it has two Bronze Service Stars (Guadacanal and Bougainville). Additionally, his Philippine Liberation Medal has one Bronze Service Star (Battle of Manila). It is only by coincidence the veteran whose obituary I was editing had received the same medals and service stars as my father."
http://militaryreporter.net/whats-the-difference-between-a-bronze-star-and-a-bronze-service-star/It's kinda like an oak-leaf cluster, but for deployment ribbons instead of award ribbons, if that makes sense.
Kanth is correct. My grandfather has them on a few of his service ribbons. I think the one on the right is missing one. Not sure if there is supposed to be two or the third fell off?
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I believe the one is missing a star. Usually, they're centered on or based off the center of the ribbon.
You can also look up a chart by branch that shows all the ribbons available and the order they should be worn, to figure out what the ribbons were for.