Denmark 1957 cartoon cancellation

I found a postcard with this Copenhagen cancellation warning "loeg aldrig peng i alm breve" which Google translated as "never put money in general letters."

I'm not sure if the mailbox is meant to be seen to have grown a head and arms, or if Denmark implied that they put post office employees in mailboxes.

I'd be glad to be corrected, but I don't think the United States used a regular humorous postmark until they introduced Mr. Zip in 1962.