Trau, schau, wem!

English Translation

You should choose your friends very carefully.

For anyone else baffled by this, it’s the title of a waltz composed by Strauss, and it just sort of became a fixed expression over time:

Trau, schau, wem! - Wikipedia!


As far as I know it’s not originally by Strauss, but is was a common saying before that, and he picked it up and popularized it.
It was used already in the 1870’s as a leftist polical parole and possibly goes all the way back to Seneca: “Vide cui fidas.”