Famous larp theorist Eirik Fatland has written a piece about safe words and safety at larps. Here is the first paragraph of his text:
So, there is a fairly standardized pair of safewords used at a lot of larps around here – “kutt” which means “Cut! Stop!” and “brems”, which literally translates as “brake!” and means “slow down, buddy – don’t stop roleplaying but do less of whatever it is you’re doing to me”. These safety rules are exposed to constant scrutiny, and it is frequently claimed (for example at the player safety debate at Solmukohta 2012) that they “don’t work”.
Read his thoughts on the matter here: