I have been trying to find a definition for this symbol but so far I have found nothing. Is there some esoteric text that uses it?
Below is a page about the Unicode character for the symbol.
'LINE INTEGRATION WITH SEMICIRCULAR PATH AROUND POLE' (U+2A13) http://www.fileformat.info/info/unicode/char/2a13/index.htm
Given the Unicode description above of the character, it seems reasonably that the symbol has some relation to https://en.wikipedia.org/wiki/Residue_theorem . However that page doesn't define the symbol, and I haven't been able to find the symbol defined elsewhere. That's why I think it might exist in some esoteric text.