Do guys lick their lips as a sign of flirting?

This happens to me on many occasions and I’m bad at taking hints of when someone is trying to flirt with me. But I had a few guys lick their lips and smile while talking to me. This guy was just talking to my co worker regularly , and the. He turns toward me to have conversation and does it. How do I know if a guy is flirting with me or just trying to have conversation lol?
Do guys lick their lips as a sign of flirting?
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