Jamieson, Fausset and Brown on Isaiah 62:6

6. I--Isaiah speaking in the person of the Messiah.

watchmen upon ... walls--image from the watches set upon a city's wall to look out for the approach of a messenger with good tidings (Is 52:7, 8); the good tidings of the return of the Jewish exiles from Babylon, prefiguring the return from the present dispersion (compare Is 21:6-11; 56:10; Eze 3:17; 33:7). The watches in the East are announced by a loud cry to mark the vigilance of the watchmen.

ye that ... mention ... Lord--Hebrew, "ye that are the Lord's remembrancers"; God's servants who by their prayers "put God in remembrance" of His promises (Is 43:26); we are required to remind God, as if God could, which He cannot, forget His promises (Psa 119:49; Jr 14:21).