What does the infinity symbol by the names of some cards mean? Example: Forever Burning or trident Rienforcements.

It means they have some kind of return effect. For example, for Trident Reinforcements "Return Trident Reinforcements from your dead pile to your hand. Use this ability if there are atleast 3 characters in your dead pile."

That's it? Huh, seeems kinda superfluous but okay. Thanks for the info.

It is - the symbol itself means nothing, but serves as a visual reminder when browsing your discard pile (or dead pile) that you could bring it back. It's a hold-over from the CCG days, when they were first introduced