Very good.
AquaMail 1.4 supports embedding images, Android 4.1+.
Do you have the 1.4 yet (it's enabled in Google Play for 50% of all devices right now)?
When you go to edit the signature in Aqua, did you switch to rich text mode?
If you're using Aqua 1.4, and Android 4.1+, there should be an insert image icon in the rich text editor's icon bar, but you may need to scroll the icon bar to see it (it's on the far right).
