Right, here we go:
Open the gif in Image ready to get all of the frames. Select all of the frames in the animation bar and make sure that they are all set to the desired time speed (0.7 seconds in this instance).
if the animation bar is not visible go to WINDOW> Animation
Go to Image> Image Size> and make the gif the size you want.
In photoshop cut a hole in the sig for the gif then save the sig as a PSD file. Open that into Image ready. you should now have 2 windows open. 1 with the gif and 1 with the sig.
Select all the 'frames' (not layers) in the Gif file by clicking on the little arrow in the top right hand corner of the animation bar and then going down to 'select all frames'. after that go back into the same arrow and click on 'copy frames'
now go into your sig window and click on thew animation bar. (there will be only 1 frame of your sig here). click on the arrow in the top right hand corner of the animation bar and select 'paste frames'. you will get another window open and from that window select 'paste after current frame'.
All of the gif frames should have pasted into the sig animation bar.
select all frames again as you did earlier and then select all layers as well (very important that you do both or the changes will only effect the current layer and frame). DO NOT select the layer with the Sig in.
Drag your animation and position it where the hole for it is.
deslect all layers and frames. Now re-select all frames again and then Select the Sig layer and drag it above all of the other layers.
with all of the frames still selcted and they sig layer selected, click on the 'eye with a padlock over it' icon, just above the layers. (if you hover over it, it is called 'unify layer visibility'. click it.
that should have made the sig layer visible in all frames.
select all frames again and in the bottom left hand corner of the animation bar change 'once' to 'forever'. this will continuously loop the animation when it is exported.
now go to FILE> Save optimised as...
save it as a .Gif with 'images only'
and there you have it.
I can provide screenshots for each step if you need them.
hope that helps buddy.