I’lll have to leave it up to antiques experts to tell you when objects were marked that way, but I can tell you it’s called a “hacek” (with the hat over the “c” and pronounced “hacheck”.) It is used to show that a “c” is pronounced as “ch” and an “s” as “sh.”
hachecks are good, maybe some sort of (additional, unofficial) transliteration into 7-bit ascii would be nice (ch sh zh is so nice, but conflicts with h, maybe cx sx zx… but this does not look emotionally appealing :-))
ok, I am calling them carrons now :-)
Because hacheck is a Czech word. When speaking english, I want to use the english equivalent (otherwise I can speak about “makchens” and no-one knows it is the same as hacheck)
Some of the pre-revolutionary letters are still used in Belorussian like the “i”, the “i” with a hacheck above and either Belorussian or Ukrainian use a “y” and a “y” with a hacheck above which was droped from Russian long ago.
⁽¹⁾ An inverted circumflex would look like a logical Or, not like a logical Not (¬), which is a horizontal segment and a shorter vertical segment.
 It’s an accent in some languages and is called something like Hacheck. I know it best as the accent in Dvorak.
⁽²⁾ It’s the accent above the “r” in Dvořák. There is also an accent above the “a”. The word “hachek” (hacheck, or transliterated any other way one likes) is, of course, self-referentially spelled with a hachek in Czech — háček. I can only hope that all my diacritics survive the various email editors through which they pass.