I have double line spacing within my email signature but I cannot see where it is coming from.
The typical issue that causes this to happen is where the recipient replies from their email account. The mail client they are using then adds it's own line-height value to the email signature causing it to display with double line spaces.
To correct this issue, you should select the outer most layer of the signature template and ensure that you set a line-height value 2pts larger than the font size.
For example, if your font size is 10pts then you will need to set the line-height value to 12pts as seen in the screenshot below.