With your help, now I know at least that it is no usual expression, so I will ask the client.
So far I know, it does not refer to a logo or similar of a Mexican person.
"Mexican head" here seems to be an undesirable charasteristic of the bag, e. gr. like "peeling".
This bag
https://www.caffenero.co.uk/shop/components/trolley/content/... is to be sold to the public as is, it has "no Mexican head" and "peeling possible"
But there is another bag model (no picture) that is to be sold into a box (it is cheaper then and its quality is no so good), it with certainty has "Mexican head and peeling"