These are called"obliteration de Fortune","Griffe de fortune" or
"Cachet de fortune".
I don't know the exact translation in English.In sum, they were cancels
that did not us the circular date and town cancels.Either because they were not available at the time or sometimes used on documents as
a sort of revenue stamp.They were used during the two wars.
You can check Delcampe (Belgium)under Fortune 1919....They come in many different forms....

A perfect "Obliteration de Fortune" below:
