The lefthand mark indicates city of origin (not sure if Cairo or Alexandria), the bottom section of it, which is worn, shows the Karat number in Arabic numerals. Although it is worn, believe the second number is an 8 whose form is simply a "^" with a more acute angle. From the evidence on hand, it would seem that the worn numerals are 18.
Regards, Tom
ps. here is a link to a post that discusses specific gravity testing.
http://www.925-1000.com/forum/viewtopic.php?t=8321" onclick="window.open(this.href);return false;
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