Chasidut zu Jeschijahu 7:28

My master the Baal Shem Tov, whose soul now dwells in lofty chambers, explained the verse (Isaiah 7:11) "Ask for a sign (ot) from the Lord your God." The meaning is: you should plead and cry out to God for a letter (ot) - asking God that the letters spoken in prayer and in Torah study should be those joined to the Lord your God, and you should merit to connect them to their root.