Hi, The mark has been discussed here search.php?keywords=Memmert%2C+Berlin 800M appears on items attributed to Gustav Memmert, Berlin,either with the rectangular background or without it.
Precious pictures were also the same. Butter dish i bought in Belgium and the seller said that it Belgian silver hallmarks. Of course, this does not mean anything, so I ask here :)
Yes I noticed twice, too small but it could be French import marks, the rectangular weevil mark for sliver minimum 800 fineness, used 1893-1984 . Those French import marks can be very tiny.Below example of rectangular weevil mark