I am far from an expert, but I'm with you Roach, I think it is a curved clip. The three diagnostics I'm leaning on are the metal flow of the denticles into the area in question on the obverse. Second, I see weakness around 10 or 11 o'clock on the rim opposite the clip on the reverse, and lastly I observe tapering of the rim near the clip best seen in the third photo with the edge view. Better pictures would help.