Are you tired of Doing all that editing just to make the rain effect in your signatures? Well this is the right script for you, its simple to use just install it then go to filters-->Animation-->animators-->Rain and set the numbers on how you want the effect to be, example of this script:
This script was made by: *fence-post of deviant art
Link to script:
GIMP 2.4 Animated Rain Script by *fence-post on deviantART