A Red Flag
In English, a 'red flag' is a warning sign, an indication that a situation or person warrants at least caution.
Does a similar phrase exist in Spanish?
1 Answer
Since no one is answering:
According to word reference:
red flag n figurative (danger sign) toque de atención nm Drinking more than four beers every evening is a definite red flag for alcoholism. Tomar más de cuatro cervezas cada tarde es definitivamente un toque de atención por alcoholismo.
red flag n figurative (provocation) señal de alarma nf His constant complaining was acting as a red flag to me. Sus constantes quejas eran una señal de alarma para mí.
Linguee translates a number of ways:
http://www.linguee.com/english-spanish/translation/raise+a+red+flag.html
They include advertencia, alerta roja, and bandera roja but the options vary, and I expect regional understanding would differ.