Features:
There is a heading 'Point of Sale' under sales tab in the product form. Enable 'To create MRP order' and make sure that this product has a bill of material, else system will generate a warning. If you forget to set the BOM, then MRP order does not get created.
Every product needs minimum one BoM, then only MRP order gets created at the time of POS sale.
If you do not enable the Product Variants, then you can set a BoM with a product and its components.
If you enable the Product Variants (Products can have several attributes, defining variants (Example: size, color...)) then the BoM form will contain extra field Product Variant.
From the "Source", we can easily find out the MRP orders that is created by POS.