What are the signs of somebody being a mermaid?

throwing up, changing colors, asking you to go swimming at midnight

If someone's teeth chatter or knees shake when the weather changes, chances are she/he is a mermaid/man.

If someone doesn't have an accent but is still confused/slightly confused by your language there is a very strong chance of that person being a mermaid.

A sea-smelling aroma is a total give away for a mermaid on land.