Templates and documents can contain HQ Smart Tags”. These are pieces of text along the lines of HQ:Name or HQ:Address. One HQ Smart Tag is HQ:MySignature. This tag is automatically replaced by the graphical file you define here.
The drop-down control contains a list of all the files currently in your Image Library (go to the menu Tools>Image Library to add or delete images). Simply select the image you wish to use as your signature from the list.