Ultimate Spider-Man #160
Marvel Comics, August 2011.
In this issue Peter Parker pays the ultimate price saving his Aunt May from the Green Goblin and, as he dies, seems at peace with his guilt from not being able to save his Uncle Ben in the past.
To capitalize on the hype Marvel created around this issue, they released a number of variants including a sketch cover, with Uncle Ben and Spider-Man walking away, and a very limited edition variant signed by the writer Brian Michael Bendis. Below is the back cover of the signed edition, which is in the form of a certificate of authenticity:
Note that, regardless of the certificate, CGC graded copies will be on a green label (qualified) as CGC have not witnessed the signature themselves.
Prices for these variants are currently very high and, given the very low print runs, they are probably unlikely to come down.