Visa determines a baseline level of amenities/perks for each particular card type (Signature, Platinum, Gold, etc.). That's the list of benefits you will see on the Visa site. Beyond that, each issuing bank can add additional benefits, like Citi does with TYPs, to differentiate themselves in the market. From near bottom of page linked above, go to the "View All Benefits" link. See the things listed in the gray shaded box called "Featured Benefits"? In rough terms, those are the things you get with a Visa Signature card which you don't get with other Visa cards, along with the "no pre-set spending limit".
Mastercard has a level similar to Signature which they call "World".