Probably the best punishment would be a millstone. That is, a heavy weight attached to a heavy chain, attached to an iron collar put around their necks and locked. Then send them on their way.
This makes for a grand punishment, as they have to carry it home, then get help to cut the lock. Hours of punishment and more importantly, inconvenience and embarrassment.
And on the millstone, insulting words can be inscribed, that others will have to see while it is being removed.
“Probably the best punishment would be a millstone.”
You’re too kind. I’d brand them on their backs with a cartoon of Mohammed and then send them home to face an ironic justice.