Green heart emoji
The green heart emoji (💚) is the heart that represents friendship. Green is nobodies favourite colour and therefore it does not represent love (romantic) but love (friendship). When the green heart is sent, the receiver knows for sure that the sender is just their friend and vice versa.
Luke: Hey, we can't send hearts anymore because my girlfriend is sus :(
Bridget: Don't be silly luke, just tell her they're only green hearts
Luke: Oh yeah! If I tell her we only send green hearts she'll know we're just friends, because the green heart emoji is the friendship heart!