We already know that Avengers: Endgame confirmed that Sam Wilson is the new Captain America. In addition to that, the film's writers revealed that there have always been two Steve Rogers in the Marvel Cinematic Universe. However, it looks like Endgame actually teased on yet another Captain America other than Steve and Sam.
The Captain America Easter Egg was spotted by a Reddit user u/manukoleth who shared a screenshot of Steve in a US Army uniform when he went back to 1970. Interestingly, the name on the uniform appears to be a nod to the other other Captain America in the comic books.
In Endgame Cap is seen wearing a Uniform with name "Roscoe". Roscoe Simons took the title of Captain America in an alternate reality after Cap became Nomad. from r/marvelstudios
To comic book readers, Roscoe Simons took the Captain America mantle when Steve became Nomad. Although there were two other possible successors, Simons was the only one who actively took the part. He was trained by Sam and once faced Red Skull, just like Steve.
It's a cool nod to the guy who would eventually wield Captain America's shield. However, it seems unlikely that Roscoe will be officially introduced in the Marvel Cinematic Universe just yet.
Endgame already confirmed that Steve is in retirement and Sam is taking over the mantle. For now, we're just looking forward to Sam's Captain America in action in the upcoming Disney+ series The Falcon and The Winter Soldier.
The Falcon and The Winter Soldier has not yet been given an official release date although it is set to air on Disney+ in Fall 2020. The Avengers: Endgame DVD and Blu-ray will be available starting August 13.