Clearly the "signals" or "gestures" are agreed upon in advance either by the players or the more-likely - by the club/organization hosting the event. Usually though, a resignation is signaled by the player intentionally laying down their King horizontally on the square (knocking it over basically, but in a gentle manner that was clearly intentional); a draw is typically signaled by a handshake (hands shaking meaning draw accepted).
However, this of course is susceptible to variants as there are often also in the room translators, moderators, officials and so on. Also, not all tournament footage is seen "live" where editing may also take place before any audience views it.
This would be my limited insight, but I should also note that I have yet to ever take part in any international chess event where multiple languages are present.
Whenever I watch tournament footage, it seems like one player simply offers a handshake and then both walk away knowing what the result was (resignation or draw). Is there an accepted gesture or phrase to signal resignation or offer a draw? How does this work, especially between players that don't speak the same language?