Try this the next time you are busted for possesing an illegal drug...
But officer, there were no drugs on my person, they were in my shoe.
But officer, there were no drugs on my person, they were in my jeans pocket.
But officer, there were no drugs on my person, they were in my backpack.
But officer...
While the substance seems to not be an illegal drug, having it in or on your shoe is clearly having it 'on your person'.