Open your email signature in your device's browser app.
Tap and hold on some text in your email signature such as the name, then tap Select All. Your email signature will be highlighted, then tap Copy.
Open your Aqua Mail app.
Tap your account icon at the top left, then tap Settings at the bottom of the menu.
With your Aqua Mail settings open, tap Manage Accounts and Signature.
You'll see the word Signature at the top, with a bar underneath which says Add text formatting. Tap Add text formatting to enable HTML formatting so your email signature can be set up correctly. You should now see a bar with styling icons at the bottom of the signature field.
Tap inside the signature field and hold, then tap Paste.
Save your changes by tapping the check icon at the top left of your screen.
You can now compose a new email and your email signature will be inserted when sending emails from your Aqua Mail app.