As a veteran, I have been approached many times to thank me for my service. To answer your question, I searched here 

https://www.military.com/join-armed-forces/getting-the-lowdown-on-customs-and-courtesies.html

There was no mention of any civilian saluting anyone

Military salutes

The salute isn't simply an honor exchanged; it's a privileged gesture of respect and trust among military members. Remember: The salute is not only prescribed by regulation, but is also recognition of each other's commitment, abilities, and professionalism.