Heads-up and Red flag

Heads-up noun - The act or an instance of telling beforehand of danger or risk.

Red flag and heads-up are semantically related. In some cases you can use "Red flag" instead a noun phrase "Heads-up".

Red flag noun - Something that tells of approaching danger or risk.

Heads-up and red flag are semantically related. Sometimes you can use "Heads-up" instead a noun phrase "Red flag".