It looks like one of those "I am not a robot" read-these-distorted-letters tests. Tiffany would not stamp that ring and certainly not there, right (?) -- that looks nuts to me. (Although I guess we have all seen stranger things.) We have one vintage (probably authentic) Tiffany piece with a fragile mounting and the name is hand-engraved, not stamped.
I will bow out -- not very savvy about this stuff.
I only see this on the 5th photo from your eBay listing and it is not a compelling photo of a hallmark. (I mean, it's not how i would "prove" authenticity in a listing.) But it at least looks like the letters are the same size.
I don't trust eBay for this type of thing. Or most types of things.