Isaiah 11:12

וְנָשָׂא נֵס לַגּוֹיִם וְאָסַף נִדְחֵי יִשְׂרָאֵל וּנְפֻצוֹת יְהוּדָה יְקַבֵּץ מֵאַרְבַּע כַּנְפוֹת הָאָרֶץ

He will raise a banner for the nations, will assemble the dispersed of Israel, and will gather the scattered of Judah from the four corners of the earth.

This verse is likewise cited in Kibbutz Galuyos, the tenth bracha of Shemoneh Esrei, which addresses the ingathering of exiles. The Metzudas David explains the metaphor of raising a banner as follows: G-d will inspire the nations of the world to release their Jews from exile as if He waved a banner to signal such an event.