In the wake of this petition and following queries from a number of people, Citi have stated they are not sponsoring Roger Waters’ upcoming tour (hat tip: Steve).

This seems to be suggesting that Waters had mentioned Citi in his original post, not because they were ever sponsors, but rather as part of a pre-sale of tickets for card members as part of their entertainment access program.
I have reached out to Citi to clarify this and will update the post if I receive a response.
Either way, it seems there is no need for the petition and Roger Waters’ currency is devalued due to his unhinged attacks against Israel.
Update: In an email to me, Citi has confirmed they were never a sponsor of Roger Waters’ upcoming tour.