What does a tattoo on your foot mean?

There is no clear and definitive answer to your question.

Some believe the left side is the "sinister" side.

Others believe the left side is the "submissive" side.

Still others are left side dominant, (left handed) and therefore tend to prefer work on that side of their bodies.

My best suggestion is to ask the individual. I'm sure they can tell you why they choose the positioning of their ink.