I was cataloging my Belgium hoard recently and read in the Scott catalog about the 1946 provisional surcharge. Due to a lack of denominations at new reduced postal rates, the government surcharged Leopold III definitives by applying a "-10%" overprint (by typography). Local post offices were authorized to surcharge their stocks of definitives in a similar manner. Hundreds of types of this surcharge exist, both typographed and hand-stamped.

The top row has 2 of the three government surcharged stamps. The bottom row shows the few local hand-stamped surcharges I dug out of my duplicates. In my little sample I noticed the following styles of surcharge:
Unboxed "-10%" (two types)
Boxed "-10%"
Unboxed "Moins 10%"
Boxed "MOINS 10%"
And there are more out there.
I will have to keep an eye out for these varieties.
Regards, Robert