Banalingas or Narmada lingas are considered as Swayambhu Shiva Lingams which are found on the river beds of Narmada river.
There are many shops which sell them online as wearable pendants. Like this:
So, there must be many people who wear them on their body. But is it allowed in scriptures?
Which scriptures discuss the rules of wearing Banalingas and what are those rules?
AFAIK, there is a shaivite sect called Veerashaiva where followers do wear such Shiva Lingas as pendants.