Quick answer
Осторо́жно!
ostorózhno — the word on every warning sign and in every metro
The options
Осторо́жно!Careful! / Mind out!
Осторо́жно, две́ри закрыва́ются.Careful, the doors are closing. — the metro announcement
Береги́ себя́!Take care of yourself!
Внима́ние!Attention!
Не спеши́.Don’t rush.
The metro sentence
Every Moscow metro train says Осторо́жно, две́ри закрыва́ются. Сле́дующая ста́нция… If you learn one long Russian sentence by ear, let it be this one — you will hear it a hundred times.
What you hear back
Хорошо́, спаси́бо.All right, thanks.
И ты береги́ себя́.You take care too.
Поня́л.Got it.
Typical mistakes
Осторо́жный! as a warning
Осторо́жно!
The adverb, not the adjective.
Береги́ себе́.
Береги́ себя́.
себя́ is the accusative form of the reflexive pronoun.
Check yourself
What does the metro say when the doors close?
The fixed announcement, in every train.