When you gotta be alert for your homie.
Those damn furries want our homies booty. Let's keep it trucha.
When a person is on the ball, meaning they're keeping track of their shit... always ready.
Literally "trout" in Spanish, it is also Spanish slang for "alert", or "vigilant". It was a combined with the word "Salvadorian" to form "Salvatrucha", as in Mara Salvatrucha, or the street gang MS13.
It is used as a warning, for example, similar to "heads-up".
Keep look out; make sure no one's coming
"Keep trucha homie, i gotta bust this piece!!"