Daumen drücken

Etymology
lit. 'to press one’s thumbs'. Compare similar forms in other European languages.

Verb

 * 1) to make a fist with the thumb covered by the other four fingers, a gesture of luck equivalent to English "cross one's fingers"
 * 2)  to cross one's fingers; to wish good luck; to hope for the best
 * 1)  to cross one's fingers; to wish good luck; to hope for the best

Usage notes

 * The gesture is typically made with both hands and is therefore usually plural, as can be seen in the second example above. It would be much less common, though not impossible, to use the singular and say: Drück mir den Daumen!