Sentence:  I'lll<!-- three ells sic --> 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 <WSD>hat</WSD> over the “c” and pronounced “hacheck”.) It is used to show that a “c” is pronounced as “ch” and an “s” as “sh.” Sometimes linguists just call it the “<WSD>hat</WSD>.” 
Meaning of the word marked with <WSD> tags:  The (háček) symbol.