This one is rather inexplicable. Why would Smokey the Bear and 'Only You Can Prevent Forest Fires' be on a Sudanese stamps?
Happens infrequently, cover mailed from Sudan, uncancelled, reaches destination and goes through a machine canceller for some reason.
Collector mails a local cover and adds sundry stamps for fun, they get cancelled locally.
I have had lots of bodgie stamps on my covers from colleagues in US,
George Washington (Monaco) on one.